chore: add missing docstrings in document store base tests

[masci]

Related Issues

• part of Docstring linting #7096

Proposed Changes:

Ignore docstrings presence for legacy tests

How did you test it?

Notes for the reviewer

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[julian-risch]

LGTM! 👍
pylint still complains about empty-docstring.

[coveralls]

Pull Request Test Coverage Report for Build 8611504773

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.842%

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Totals
Change from base Build 8603659000:	0.0%
Covered Lines:	6023
Relevant Lines:	6704

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💛 - Coveralls