feat: next release from main branch is 3.1.0 (#910)

Author: suztomo

.github/release-please.yml

@@ -18,3 +18,7 @@ branches:
     handleGHRelease: true
     bumpMinorPreMajor: true
     branch: 2.10.x
+  - releaseType: java-backport
+    handleGHRelease: true
+    bumpMinorPreMajor: true
+    branch: 3.0.x

.github/sync-repo-settings.yaml

@@ -76,6 +76,21 @@ branchProtectionRules:
       - 'Kokoro - Test: Integration'
       - cla/google
       - OwlBot Post Processor
+  - pattern: 3.0.x
+    isAdminEnforced: true
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: false
+    requiredStatusCheckContexts:
+      - dependencies (8)
+      - dependencies (11)
+      - lint
+      - clirr
+      - units (8)
+      - units (11)
+      - 'Kokoro - Test: Integration'
+      - cla/google
+      - OwlBot Post Processor
 permissionRules:
   - team: yoshi-admins
     permission: admin