feat: next release from main branch is 1.21.0 (#1372)

Co-authored-by: Diego Marquez <[email protected]>

Author: lqiu96

.github/release-please.yml

@@ -26,3 +26,7 @@ branches:
     handleGHRelease: true
     releaseType: java-backport
     branch: 1.19.x
+  - bumpMinorPreMajor: true
+    handleGHRelease: true
+    releaseType: java-backport
+    branch: 1.20.x

.github/sync-repo-settings.yaml

@@ -93,6 +93,18 @@ branchProtectionRules:
     requiredApprovingReviewCount: 1
     requiresCodeOwnerReviews: true
     requiresStrictStatusChecks: true
+  - pattern: 1.20.x
+    isAdminEnforced: true
+    requiredStatusCheckContexts:
+      - dependencies (17)
+      - lint
+      - clirr
+      - units (8)
+      - units (11)
+      - cla/google
+    requiredApprovingReviewCount: 1
+    requiresCodeOwnerReviews: true
+    requiresStrictStatusChecks: true
 permissionRules:
   - team: Googlers
     permission: pull