Bump cygwin/cygwin-install-action from 5 to 6

Bumps [cygwin/cygwin-install-action](https://github.com/cygwin/cygwin-install-action) from 5 to 6.
- [Release notes](https://github.com/cygwin/cygwin-install-action/releases)
- [Commits](cygwin/cygwin-install-action@v5...v6)

---
updated-dependencies:
- dependency-name: cygwin/cygwin-install-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/cygwin-test.yml

@@ -39,7 +39,7 @@ jobs:
         fetch-depth: 0
 
     - name: Install Cygwin
-      uses: cygwin/cygwin-install-action@v5
+      uses: cygwin/cygwin-install-action@v6
       with:
         packages: git python39 python-pip-wheel python-setuptools-wheel python-wheel-wheel
         add-to-path: false  # No need to change $PATH outside the Cygwin environment.