build: update required checks (#821)

Author: Justin Poehnelt

.github/sync-repo-settings.yaml

@@ -24,13 +24,19 @@ branchProtectionRules:
   requiresStrictStatusChecks: false
   requiredStatusCheckContexts:
     - 'cla/google'
+    - 'test'
+    - 'snippet-bot-check'
+    - 'header-check'
   requiredApprovingReviewCount: 1
   requiresCodeOwnerReviews: true
 - pattern: master
   isAdminEnforced: false
   requiresStrictStatusChecks: false
   requiredStatusCheckContexts:
     - 'cla/google'
+    - 'test'
+    - 'snippet-bot-check'
+    - 'header-check'
   requiredApprovingReviewCount: 1
   requiresCodeOwnerReviews: true
 permissionRules: