Add BROWSERSLIST_IGNORE_OLD_DATA env var during build.

Author: iclanton

common/config/azure-pipelines/templates/build.yaml

@@ -13,3 +13,7 @@ steps:
     displayName: 'Rush Install'
   - script: 'node common/scripts/install-run-rush.js rebuild --verbose --production'
     displayName: 'Rush Rebuild'
+    env:
+      # Prevent time-based browserslist update warning
+      # See https://github.com/microsoft/rushstack/issues/2981
+      BROWSERSLIST_IGNORE_OLD_DATA: 1