Bump slotscheck from 0.20.1 to 0.21.0 (#2509)

Bumps [slotscheck](https://github.com/ariebovenberg/slotscheck) from 0.20.1 to 0.21.0.
- [Release notes](https://github.com/ariebovenberg/slotscheck/releases)
- [Changelog](https://github.com/ariebovenberg/slotscheck/blob/main/CHANGELOG.rst)
- [Commits](ariebovenberg/slotscheck@v0.20.1...v0.21.0)

---
updated-dependencies:
- dependency-name: slotscheck
  dependency-version: 0.21.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

poetry.lock

@@ -65,7 +65,7 @@ trio = ">=0.33,<0.35"
 attrs = "^26.1"
 httpx = "^0.28"
 wemake-python-styleguide = "^1.7"
-slotscheck = "^0.20"
+slotscheck = ">=0.20,<0.22"
 ruff = "^0.16"
 pytest-cov = "^7.1"
 pytest-randomly = ">=4.1,<6.0"