Use pinned SHA for action reference

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: jeffhandley

.github/workflows/copilot-setup-steps.yml

@@ -11,7 +11,7 @@ jobs:
       contents: read
 
     steps:
-      - uses: actions/checkout@v6.0.0
+      - uses: actions/checkout@1af3b93b6815bc44a9784bd300feb67ff0d1eeb3 # v6.0.0
 
       - name: Install .NET SDK
         uses: actions/setup-dotnet@v5.0.1