microsoft/setup-msbuild: pin sha1

Author: jpnurmi

.github/workflows/build.yml

@@ -245,7 +245,7 @@ jobs:
         uses: ./.github/actions/buildnative
 
       - name: Add MSBuild to PATH
-        uses: microsoft/setup-msbuild@v2
+        uses: microsoft/setup-msbuild@6fb02220983dee41ce7ae257b6f4d8f9bf5ed4ce # v2
 
       - name: Run MSBuild
         id: msbuild