ci: use pinned version for google-github-actions/auth action

Author: clydin

.github/workflows/perf.yml

@@ -45,7 +45,7 @@ jobs:
       # identity federation. This allows us to request short lived credentials on demand, rather than storing
       # credentials in secrets long term. More information can be found at:
       # https://docs.github.com/en/actions/security-for-github-actions/security-hardening-your-deployments/configuring-openid-connect-in-google-cloud-platform
-      - uses: 'google-github-actions/auth@v2'
+      - uses: google-github-actions/auth@6fc4af4b145ae7821d527454aa9bd537d1f2dc5f # v2.1.7
         with:
           project_id: 'internal-200822'
           workload_identity_provider: 'projects/823469418460/locations/global/workloadIdentityPools/measurables-tracking/providers/angular'