feat: next release from main branch is 6.89.0 (#3669)

Author: ldetmer

.github/release-please.yml

@@ -42,3 +42,7 @@ branches:
     bumpMinorPreMajor: true
     handleGHRelease: true
     branch: 6.66.x
+  - releaseType: java-backport
+    bumpMinorPreMajor: true
+    handleGHRelease: true
+    branch: 6.88.x

.github/sync-repo-settings.yaml

@@ -161,6 +161,27 @@ branchProtectionRules:
       - compile (11)
       - units-with-multiplexed-session (8)
       - units-with-multiplexed-session (11)
+  - pattern: 6.88.x
+    isAdminEnforced: true
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: false
+    requiredStatusCheckContexts:
+      - dependencies (17)
+      - lint
+      - javadoc
+      - units (8)
+      - units (11)
+      - 'Kokoro - Test: Integration'
+      - 'Kokoro - Test: Integration with Multiplexed Sessions'
+      - cla/google
+      - checkstyle
+      - compile (8)
+      - compile (11)
+      - units-with-multiplexed-session (8)
+      - units-with-multiplexed-session (11)
+      - unmanaged_dependency_check
+      - library_generation
 permissionRules:
   - team: yoshi-admins
     permission: admin