Build ref-protection plugin on its own stable-3.0 and stable-3.1 branches

Change-Id: I2e3342fe79183678c9787b78110b2e562d103af3
diff --git a/jenkins/gerrit-bazel-plugin-ref-protection.yaml b/jenkins/gerrit-bazel-plugin-ref-protection.yaml
index 9741592..0253a4d 100644
--- a/jenkins/gerrit-bazel-plugin-ref-protection.yaml
+++ b/jenkins/gerrit-bazel-plugin-ref-protection.yaml
@@ -6,9 +6,8 @@
             - master
           gerrit-branch:
             - master
-            - stable-3.1
-            - stable-3.0
       - 'plugin-{name}-bazel-{branch}':
           branch:
-            - master
+            - stable-3.1
+            - stable-3.0
             - stable-2.16