Use double quotes for all docstrings, including single-quoted docstrings

[MichaReiser]

Summary

This PR changes our docstring formatting to enforce double quotes for single-quoted docstrings (and not just triple-quoted strings).

I see reasons for and against this.

• We enforce an empty line after all docstring, regardless if they are single or triple quoted. Meaning, we recognize single-quoted string literals as docstrings (according to PEP 257). This speaks in favor of enforcing double quotes
• The quote-style documentation mentions that it enforces double quotes for all docstring, but this isn't the case without this PR.
• PEP 257 recommends using triple double quotes for all docstrings, but this PR only enforces using double quotes, but not using triple quotes. Meaning, the result is only half-correct.

Alternatives:

• Leave as is
• Be even more opinionated and change quotes to triple quotes

I favor the consistency of what we consider docstrings and how we format them.

Test Plan

Added test

[MichaReiser]

Current dependencies on/for this PR:

• main
  • PR Enforce valid format options in spec tests #9021
    • PR Use double quotes for all docstrings, including single-quoted docstrings #9020 👈

This stack of pull requests is managed by Graphite.

[github-actions]

ruff-ecosystem results

Formatter (stable)

✅ ecosystem check detected no format changes.

Formatter (preview)

✅ ecosystem check detected no format changes.

[konstin]

Be even more opinionated and change quotes to triple quotes

I'd favor this, because single quotes obfuscate that the statement is a docstring