Bump ruff from 0.15.18 to 0.15.20 in /stash (#1005)

Bumps [ruff](https://github.com/astral-sh/ruff) from 0.15.18 to 0.15.20.
- [Release notes](https://github.com/astral-sh/ruff/releases)
- [Changelog](https://github.com/astral-sh/ruff/blob/main/CHANGELOG.md)
- [Commits](astral-sh/ruff@0.15.18...0.15.20)

---
updated-dependencies:
- dependency-name: ruff
  dependency-version: 0.15.20
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

stash/pyproject.toml

@@ -55,7 +55,7 @@ dependencies = []
 # desired, alongside `python3 test_*.py`.
 [dependency-groups]
 dev = [
-    "ruff>=0.15.18",
+    "ruff>=0.15.20",
     "mypy>=2.1.0",
     "pytest>=9.1.1",
 ]