pytest: fix mocker as context manager and setenv test warnings

[mattseddon]

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  guide.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here.

Thank you for the contribution - we'll try to review it as soon as possible. 🙏

---

Fixes issue of the format:

  /dvclive/tests/test_dvc.py:160: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=None):

&

  /dvclive/tests/test_main.py:229: PytestWarning: Value of environment variable DVCLIVE_RESUME type should be str, but got True (type: bool); converted to str implicitly
    monkeypatch.setenv(env.DVCLIVE_RESUME, True)

Result of pytest -v tests --ignore=tests/test_frameworks:

Before

Log

================================================================================================================================================ warnings summary ================================================================================================================================================
tests/test_dvc.py::test_exp_save_skip_on_env_vars
  /dvclive/tests/test_dvc.py:160: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=None):

tests/test_dvc.py::test_exp_save_run_on_dvc_repro
  /dvclive/tests/test_dvc.py:179: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=dvc_repo):

tests/test_dvc.py::test_exp_save_with_dvc_files
  /dvclive/tests/test_dvc.py:221: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=dvc_repo):

tests/test_dvc.py::test_no_scm_repo
  /dvclive/tests/test_dvc.py:319: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=dvc_repo):

tests/test_main.py::test_resume_env_var
  /dvclive/tests/test_main.py:229: PytestWarning: Value of environment variable DVCLIVE_RESUME type should be str, but got True (type: bool); converted to str implicitly
    monkeypatch.setenv(env.DVCLIVE_RESUME, True)

tests/test_report.py::test_make_report_open
  /dvclive/tests/test_report.py:125: PytestWarning: Value of environment variable DVCLIVE_OPEN type should be str, but got True (type: bool); converted to str implicitly
    monkeypatch.setenv(DVCLIVE_OPEN, True)

tests/test_vscode.py::test_vscode_dvclive_step_completed_signal_file[True]
  /dvclive/tests/test_vscode.py:22: PytestWarning: Value of environment variable DVC_ROOT type should be str, but got PosixPath('/private/var/folders/sb/fqcw44jd19nfrhl_9lz_81d80000gn/T/pytest-of/pytest-138/test_vscode_dvclive_step_compl0') (type: PosixPath); converted to str implicitly
    monkeypatch.setenv(env.DVC_ROOT, tmp_dir)

tests/test_vscode.py::test_vscode_dvclive_step_completed_signal_file[True]
tests/test_vscode.py::test_vscode_dvclive_step_completed_signal_file[False]
  /dvclive/tests/test_vscode.py:33: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=dvc_repo), mocker.patch(

tests/test_vscode.py::test_vscode_dvclive_only_signal_file[True]
tests/test_vscode.py::test_vscode_dvclive_only_signal_file[False]
  /dvclive/tests/test_vscode.py:78: PytestMockWarning: Mocks returned by pytest-mock do not need to be used as context managers. The mocker fixture automatically undoes mocking at the end of a test. This warning can be ignored if it was triggered by mocking a context manager. https://pytest-mock.readthedocs.io/en/latest/remarks.html#usage-as-context-manager
    with mocker.patch("dvclive.live.get_dvc_repo", return_value=dvc_repo), mocker.patch(

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

Results (4.52s):
     174 passed

After

Results (4.75s):
     174 passed

[codecov-commenter]

Codecov Report

Patch coverage is 100.00% of modified lines.

Files Changed	Coverage
tests/test_dvc.py	100.00%
tests/test_main.py	100.00%
tests/test_report.py	100.00%
tests/test_vscode.py	100.00%

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[daavoo]

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