Update status check for all supported on.pull_request.types in Gitea (#33117)

Thanks @Zettat123
Follow #33116
Fix #33051

on.pull_request.types doc:

https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#pull_request

on.pull_request.types added in this PR:
```
assigned, unassigned, review_requested, review_request_removed, milestoned, demilestoned, labeled, unlabeled
```

unsupported types in Gitea:
```
// Unsupported activity types:
// converted_to_draft, ready_for_review, locked, unlocked, auto_merge_enabled, auto_merge_disabled, enqueued, dequeued
```

TODO:
- [x] add test

modules/webhook/type.go

@@ -69,6 +69,10 @@ func (h HookEventType) Event() string {
 	return ""
 }
 
+func (h HookEventType) IsPullRequest() bool {
+	return h.Event() == "pull_request"
+}
+
 // HookType is the type of a webhook
 type HookType = string