deps-dev: update packaging requirement from >=22.0 to >=26.3

Updates the requirements on [packaging](https://github.com/pypa/packaging) to permit the latest version.
- [Release notes](https://github.com/pypa/packaging/releases)
- [Changelog](https://github.com/pypa/packaging/blob/main/CHANGELOG.rst)
- [Commits](pypa/packaging@22.0...26.3)

---
updated-dependencies:
- dependency-name: packaging
  dependency-version: '26.3'
  dependency-type: direct:development
...

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

Author: dependabot[bot]

requirements-dev.txt

@@ -16,7 +16,7 @@
 mypy>=1.11.0
 # Imported directly by the offline tests, which evaluate requirements.txt's
 # version markers the way an installer does. The floor is pytest's own.
-packaging>=22.0
+packaging>=26.3
 # 9.0.3 rather than 8.x: the 8.3.0 floor is affected by CVE-2025-71176
 # (insecure temporary directory handling). Caught by this repo's own audit gate.
 pytest>=9.0.3