build: don't require all reviewers to approve PRs (#22363)

This setting has been causing friction on PRs, requiring reviewers to be
manually approved. The "merge ready" label should only be applied once
a PR is approved.

Author: jelbourn

.github/angular-robot.yml

@@ -40,7 +40,7 @@ merge:
     # whether the PR shouldn't have a conflict with the base branch
     noConflict: true
     # whether the PR should have all reviews completed.
-    requireReviews: true
+    requireReviews: false
     # list of labels that a PR needs to have, checked with a regexp (e.g. "PR target:" will work for the label "PR target: master")
     requiredLabels:
       - "target: *"