feat: next release from main branch is 3.16.0 (#3037)

Author: jinseopkim0

.github/release-please.yml

@@ -34,3 +34,7 @@ branches:
     handleGHRelease: true
     releaseType: java-backport
     branch: 3.11.x
+  - bumpMinorPreMajor: true
+    handleGHRelease: true
+    releaseType: java-backport
+    branch: 3.15.x

.github/sync-repo-settings.yaml

@@ -132,6 +132,22 @@ branchProtectionRules:
       - javadoc
       - library_generation
       - unmanaged_dependency_check
+  - pattern: 3.15.x
+    isAdminEnforced: true
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: false
+    requiredStatusCheckContexts:
+      - dependencies (17)
+      - lint
+      - clirr
+      - units (8)
+      - units (11)
+      - 'Kokoro - Test: Integration'
+      - cla/google
+      - javadoc
+      - library_generation
+      - unmanaged_dependency_check
 permissionRules:
   - team: yoshi-admins
     permission: admin