Fix RBE platform for gerrit pipeline (#1829)

Closes #1820.
diff --git a/pipelines/gerrit.yml b/pipelines/gerrit.yml
index 321d63f..0f39cf1 100644
--- a/pipelines/gerrit.yml
+++ b/pipelines/gerrit.yml
@@ -25,12 +25,14 @@
   rbe_ubuntu2204:
     build_flags:
       - "--config=remote"
+      - "--remote_instance_name=projects/bazel-untrusted/instances/default_instance"
       - "--remote_executor=grpcs://remotebuildexecution.googleapis.com"
     build_targets:
       - "//:release"
       - "//:api-skip-javadoc"
     test_flags:
       - "--config=remote"
+      - "--remote_instance_name=projects/bazel-untrusted/instances/default_instance"
       - "--remote_executor=grpcs://remotebuildexecution.googleapis.com"
       - "--experimental_remote_cache_async"
       - "--experimental_remote_merkle_tree_cache"