Python >= 3.6 tests failing due to PyYAML 6.0

[mschfh]

Describe the bug

PyYAML 6.0 was recently released for Python 3.6 and up, which causes tests for these versions to fail due to a breaking change:
https://github.com/yaml/pyyaml/blob/8cdff2c80573b8be8e8ad28929264a913a63aa33/CHANGES#L17

always require Loader arg to yaml.load()

log:

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    Traceback (most recent call last):

      File "/opt/hostedtoolcache/Python/3.6.15/x64/lib/python3.6/unittest/mock.py", line 1183, in patched
    return func(*args, **keywargs)

      File "/home/runner/work/bandit/bandit/tests/unit/formatters/test_yaml.py", line 73, in test_report
    data = yaml.load(f.read())

    TypeError: load() missing 1 required positional argument: 'Loader'

requirements.txt specifies PyYAML>=5.3.1, replacing it with PyYAML>=5.3.1, <6.0 resolves the problem

Reproduction steps

run tests with Python 3.6 or up

Expected behavior

tests are passing

Bandit version

1.7.0 (Default)

Python version

3.6

Additional context

No response