chore: require CODEOWNER review and up to date branches (#356)

These two lines bring the rules on this repo in line with the defaults:

https://github.com/googleapis/repo-automation-bots/blob/63c858e539e1f4d9bb8ea66e12f9c0a0de5fef55/packages/sync-repo-settings/src/required-checks.json#L40-L50

Author: busunkim96

packages/google-cloud-dialogflow/.github/sync-repo-settings.yaml

@@ -4,10 +4,12 @@ branchProtectionRules:
 # Identifies the protection rule pattern. Name of the branch to be protected.
 # Defaults to `master`
 - pattern: master
+  requiresCodeOwnerReviews: true
+  requiresStrictStatusChecks: true
   requiredStatusCheckContexts:
     - 'Kokoro'
     - 'cla/google'
     - 'Samples - Lint'
     - 'Samples - Python 3.6'
     - 'Samples - Python 3.7'
-    - 'Samples - Python 3.8' 
+    - 'Samples - Python 3.8'