deps(pip): update ruff requirement from >=0.15.18 to >=0.15.21

[dependabot]

Updates the requirements on ruff to permit the latest version.

Release notes

Sourced from ruff's releases.

0.15.21

Release Notes

Released on 2026-07-09.

Preview features

• Add --add-ignore for adding ruff:ignore comments (#26346)
• [flake8-comprehensions] Drop C409 tuple comprehension preview behavior (#25707)
• Avoid whitespace normalization when formatting comments (#26455)
• [pyupgrade] Lint and fix use of deprecated abc decorators (UP051) (#26417)

Bug fixes

• Refine non-empty f-string detection (#26526)
• Detect syntax errors in individual notebook cells (#26419)
• [flake8-implicit-str-concat] Fix ISC003 autofix incorrectly stripping + from comments (#26554)

Rule changes

• [flake8-executable] Mark EXE004 fix as unsafe (#26033)
• [flake8-pyi] Mark PYI061 fixes as unsafe in Python files (#26533)
• [pydocstyle] Skip overload-with-docstring in stub files (D418) (#26318)

Performance

• Avoid per-token source index visitor calls (#26506)
• Cache parenthesized expression boundaries in the formatter (#26344)
• Improve performance of rendering edits in preview mode (#26565)
• Inline fits_element in formatter (#26429)
• Inline formatter printing hot paths (#26504)
• Lazily create builtin bindings (#26510)
• Skip empty trivia scans in the source indexer (#26507)
• Use ICF for macOS release builds (#25780)

Formatter

• Add --extend-exclude to ruff format (#26372)

Documentation

• Add "How does Ruff's import sorting compare to isort?" link to README (#26530)
• Fix Mozilla Firefox repository link in README (#26537)
• [flake8-bandit] Fix misleading docstring for mako-templates (S702) (#26432)
• [ruff] Fix non-triggering example for if-key-in-dict-del (RUF051) (#26433)

Contributors

• @​EkriirkE
• @​tingerrr

... (truncated)

Changelog

Sourced from ruff's changelog.

0.15.21

Released on 2026-07-09.

Preview features

• Add --add-ignore for adding ruff:ignore comments (#26346)
• [flake8-comprehensions] Drop C409 tuple comprehension preview behavior (#25707)
• Avoid whitespace normalization when formatting comments (#26455)
• [pyupgrade] Lint and fix use of deprecated abc decorators (UP051) (#26417)

Bug fixes

• Refine non-empty f-string detection (#26526)
• Detect syntax errors in individual notebook cells (#26419)
• [flake8-implicit-str-concat] Fix ISC003 autofix incorrectly stripping + from comments (#26554)

Rule changes

• [flake8-executable] Mark EXE004 fix as unsafe (#26033)
• [flake8-pyi] Mark PYI061 fixes as unsafe in Python files (#26533)
• [pydocstyle] Skip overload-with-docstring in stub files (D418) (#26318)

Performance

• Avoid per-token source index visitor calls (#26506)
• Cache parenthesized expression boundaries in the formatter (#26344)
• Improve performance of rendering edits in preview mode (#26565)
• Inline fits_element in formatter (#26429)
• Inline formatter printing hot paths (#26504)
• Lazily create builtin bindings (#26510)
• Skip empty trivia scans in the source indexer (#26507)
• Use ICF for macOS release builds (#25780)

Formatter

• Add --extend-exclude to ruff format (#26372)

Documentation

• Add "How does Ruff's import sorting compare to isort?" link to README (#26530)
• Fix Mozilla Firefox repository link in README (#26537)
• [flake8-bandit] Fix misleading docstring for mako-templates (S702) (#26432)
• [ruff] Fix non-triggering example for if-key-in-dict-del (RUF051) (#26433)

Contributors

• @​EkriirkE
• @​tingerrr
• @​s-rigaud

... (truncated)

Commits

• 3e1f636 Bump 0.15.21 (#26676)
• 4059807 [ty] Infer metaclass-declared attributes on class instances (#26512)
• 013e5d0 [ty] Use a dedicated project name type (#26665)
• 7ad39ad [ty] Avoid allocating decorated parameter names (#26666)
• c36f662 Improve performance of rendering edits in preview mode (#26565)
• ad26408 [ty] Gate membership narrowing on __contains__ semantics (#25964)
• 4594ca7 [ty] Add variant discriminators for CodeGeneratorKind (#26659)
• 1af03da [ty] Pydantic: Fix float conversion in unions (#26655)
• a004a36 [ty] Handle callable classes in solver (#26090)
• d8ef3b0 [ty] Parse all supported Google docstring sections. (#26653)
• Additional commits viewable in compare view