Use semantic version tag for setup-dotnet action

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

.github/copilot-setup-steps.yml

@@ -1,5 +1,5 @@
 name: Setup .NET SDK
 steps:
-  - uses: actions/setup-dotnet@d4c94342e560b34958eacfc5d055d21461ed1c5d # v5.0.0
+  - uses: actions/setup-dotnet@v5
     with:
       global-json-file: global.json