Bump clang-format from 18.1.8 to 21.1.8

Bumps [clang-format](https://github.com/ssciwr/clang-format-wheel) from 18.1.8 to 21.1.8.
- [Release notes](https://github.com/ssciwr/clang-format-wheel/releases)
- [Commits](ssciwr/clang-format-wheel@v18.1.8...v21.1.8)

---
updated-dependencies:
- dependency-name: clang-format
  dependency-version: 21.1.8
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

pyproject.toml

@@ -9,7 +9,7 @@ dependencies = []
 [dependency-groups]
 dev = [
     "cmake==4.2.1",
-    "clang-format==18.1.8",
+    "clang-format==21.1.8",
     "gcovr>=7.2",
     "pre-commit>=3.7.1",
 ]