Fix missing commit status in PR which from forked repo (#23351)

close: #23347

### Reference and Inference
According to Github REST API
[doc](https://docs.github.com/en/rest/commits/statuses?apiVersion=2022-11-28#list-commit-statuses-for-a-reference):
1. The `Drone CI` that can create some commit status by
[API](https://docs.github.com/en/rest/commits/statuses?apiVersion=2022-11-28#create-a-commit-status)
is enabled in `go-gitea/gitea`. So I tried to call the API to get a
commit status list of a PR which is commited to upstream
repo(`go-gitea/gitea`). As a result, the API returned a array of commit
status.

![image](https://user-images.githubusercontent.com/33891828/223913371-313d047a-5e2e-484c-b13e-dcd38748703e.png)
2. Then I tried to call the API to get commit status list of the
reference which of the `SHA` is the same as step 1 in the repo which is
forked from `go-gitea/gitea`. But I got a empty array.

![image](https://user-images.githubusercontent.com/33891828/223930827-17a64d3c-f466-4980-897c-77fe386c4d3b.png)

So, I believe it that：
1. The commit status is not shared between upstream repo and forked
repo.
2. The coomit status is bound to a repo that performs actions. (Gitea's
logic is the same)

### Cause
During debugging, I found it that commit status are not stored in the DB
as expected.
So, I located the following code:

https://github.com/go-gitea/gitea/blob/8cadd51bf295e6ff36ac36efed68cc5de34c9382/services/actions/commit_status.go#L18-L26
When I create a PR, the type of `event` is `pull request`, not `push`.
So the code return function directly.

### Screenshot

![image](https://user-images.githubusercontent.com/33891828/223939339-dadf539c-1fdd-40c4-96e9-2e4fa733f531.png)

![image](https://user-images.githubusercontent.com/33891828/223939519-edb02bf0-2478-4ea5-9366-be85468f02db.png)

![image](https://user-images.githubusercontent.com/33891828/223939557-ec6f1375-5536-400e-8987-fb7d2fd452fa.png)



### Other 
In this PR, I also fix the problem of missing icon which represents
running in PRs list.

![image](https://user-images.githubusercontent.com/33891828/223939898-2a0339e4-713f-4c7b-9d99-2250a43f3457.png)

![image](https://user-images.githubusercontent.com/33891828/223939979-037a975f-5ced-480c-bac7-0ee00ebfff4b.png)

models/actions/run.go

@@ -128,6 +128,17 @@ func (run *ActionRun) GetPushEventPayload() (*api.PushPayload, error) {
 	return nil, fmt.Errorf("event %s is not a push event", run.Event)
 }
 
+func (run *ActionRun) GetPullRequestEventPayload() (*api.PullRequestPayload, error) {
+	if run.Event == webhook_module.HookEventPullRequest {
+		var payload api.PullRequestPayload
+		if err := json.Unmarshal([]byte(run.EventPayload), &payload); err != nil {
+			return nil, err
+		}
+		return &payload, nil
+	}
+	return nil, fmt.Errorf("event %s is not a pull request event", run.Event)
+}
+
 func updateRepoRunsNumbers(ctx context.Context, repo *repo_model.Repository) error {
 	_, err := db.GetEngine(ctx).ID(repo.ID).
 		SetExpr("num_action_runs",