Update Cygwin install action to version 6

Author: Harvester57

.github/workflows/CI-cygwin.yml

@@ -42,7 +42,7 @@ jobs:
           persist-credentials: false
 
       - name: Set up Cygwin
-        uses: cygwin/cygwin-install-action@b9bf9147075ee9811ac11beee9351eeb93e2f2fb # master
+        uses: cygwin/cygwin-install-action@f2009323764960f80959895c7bc3bb30210afe4d # v6
         with:
           platform: ${{ matrix.platform }}
           packages: ${{ matrix.packages }}