Update ansible-lint to 6.20.2 and fix a report issue on excluded files

[TamiTakamiya]

For AAP-16692.

This PR contains three changes:

• Upgrade ansible-lint from 6.20.1 to 6.20.2
• Added the .coveragerc file not to include test case files in the code coverage calculation
• Fix an issue in reporting (report.txt) on the list of excluded files, in the "Issues found by ansible-lint" section. While it should include the files excluded from the second ansible-lint execution, it included the files that contained lint errors in the second execution as well.

[TamiTakamiya]

Without # pylint: disable=preferred-module, pylint failed with

src/ansible_content_parser/__main__.py:8:0: W0407: Prefer importing 'pathlib' instead of 'py' (preferred-module)

I don't understand the message as it complains about the py module, not the copy module specified here.
So I just added the comment to disable the rule on this line.

[gebhardtr]

Appears to be a regression: pylint-dev/pylint#8453