Try fetching tags

Author: ldionne

.github/workflows/libcxx-build-and-test.yaml

@@ -292,6 +292,7 @@ jobs:
       - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
         with:
           fetch-depth: 0 # This job requires access to all the Git branches so it can diff against (usually) main
+          fetch-tags: true
       - name: benchmarks
         run: libcxx/utils/ci/run-buildbot benchmark-comparison
         env: