Add pytest 7 compatibility

[dmkoch]

What action do you want to perform

Trying to use pytest-elasticsearch==2.1.0 with pytest==7.0.0

What are the results

pytest run crashes with:

  File "/usr/local/lib/python3.9/site-packages/pytest_elasticsearch/factories.py", line 26, in <module>
    from _pytest.tmpdir import TempdirFactory
ImportError: cannot import name 'TempdirFactory' from '_pytest.tmpdir' (/usr/local/lib/python3.9/site-packages/_pytest/tmpdir.py)

What are the expected results

pytest-elasticsearch works with pytest 7.0+

[fizyk]

@dmkoch the tmpdir_factory fixture with tmp_path_factory fixture.

The minimum supported pytest version should then be set to 6.2
ref: ClearcodeHQ/pytest-postgresql#533

[fizyk]

added