Fix deprecation warnings and a coverage warning

[hugovk]

Fixes five warnings:

.tox/py310/lib/python3.10/site-packages/coverage/inorout.py:446
  /private/tmp/oauthlib/.tox/py310/lib/python3.10/site-packages/coverage/inorout.py:446: CoverageWarning: --include is ignored because --source is set (include-ignored)
    self.warn("--include is ignored because --source is set", slug="include-ignored")

tests/oauth2/rfc6749/endpoints/test_error_responses.py::ErrorResponseTest::test_invalid_request_duplicate_params
  /private/tmp/oauthlib/tests/oauth2/rfc6749/endpoints/test_error_responses.py:181: DeprecationWarning: Please use assertRaisesRegex instead.
    self.assertRaisesRegexp(errors.InvalidRequestFatalError,

tests/oauth2/rfc6749/endpoints/test_error_responses.py::ErrorResponseTest::test_invalid_request_duplicate_params
  /private/tmp/oauthlib/tests/oauth2/rfc6749/endpoints/test_error_responses.py:185: DeprecationWarning: Please use assertRaisesRegex instead.
    self.assertRaisesRegexp(errors.InvalidRequestFatalError,

tests/oauth2/rfc6749/endpoints/test_error_responses.py::ErrorResponseTest::test_invalid_request_duplicate_params
  /private/tmp/oauthlib/tests/oauth2/rfc6749/endpoints/test_error_responses.py:191: DeprecationWarning: Please use assertRaisesRegex instead.
    self.assertRaisesRegexp(errors.InvalidRequestFatalError,

tests/oauth2/rfc6749/endpoints/test_error_responses.py::ErrorResponseTest::test_invalid_request_duplicate_params
  /private/tmp/oauthlib/tests/oauth2/rfc6749/endpoints/test_error_responses.py:195: DeprecationWarning: Please use assertRaisesRegex instead.
    self.assertRaisesRegexp(errors.InvalidRequestFatalError,

Checked tests pass locally via tox for lowest supported Python 3.6 and highest 3.9 (and 3.10).

[auvipy]

thanks!