Update gcovr requirement from >=7.2 to >=8.6

Updates the requirements on [gcovr](https://github.com/gcovr/gcovr) to permit the latest version.
- [Release notes](https://github.com/gcovr/gcovr/releases)
- [Changelog](https://github.com/gcovr/gcovr/blob/main/CHANGELOG.rst)
- [Commits](gcovr/gcovr@7.2...8.6)

---
updated-dependencies:
- dependency-name: gcovr
  dependency-version: '8.6'
  dependency-type: direct:development
...

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

Author: dependabot[bot]

pyproject.toml

@@ -10,7 +10,7 @@ dependencies = []
 dev = [
     "cmake==4.3.1",
     "clang-format==22.1.3",
-    "gcovr>=7.2",
+    "gcovr>=8.6",
     "pre-commit>=3.7.1",
 ]