ci/github-script/check-target-branch: do not "Request changes"

You can technically have multiple reviews requesting changes, but
there's no good way to dismiss all of the reviews requesting changes from
the same user using the UI.

This makes minimization impossible (because all but one of the reviews is not
dismissed, even though the PR is no longer blocked due to the review
in GitHub's system).

As a workaround, we will only comment.

CI will still fail when appropriate.

ci/github-script/check-target-branch.js

@@ -137,7 +137,7 @@ async function checkTargetBranch({ github, context, core, dry }) {
       core,
       dry,
       body,
-      event: 'REQUEST_CHANGES',
+      event: 'COMMENT',
       reviewKey,
     })
 
@@ -165,7 +165,7 @@ async function checkTargetBranch({ github, context, core, dry }) {
       core,
       dry,
       body,
-      event: 'REQUEST_CHANGES',
+      event: 'COMMENT',
       reviewKey,
     })