Fix wrong commit status in web ui (#26121)

Before:

![image](https://github.com/go-gitea/gitea/assets/18380374/8c5643b5-5c16-4674-9fe6-9e7fa2dda0b9)
After:

![image](https://github.com/go-gitea/gitea/assets/18380374/caf8891b-14df-418d-a7eb-977b54b9e9be)

There's a bug in the recent logic, `CalcCommitStatus` will always return
the first item of `statuses` or error status, because `state` is defined
with default value which should be `CommitStatusSuccess`

Then
``` golang
if status.State.NoBetterThan(state) {
```
this `if` will always return false unless `status.State =
CommitStatusError` which makes no sense.
So `lastStatus` will always be `nil` or error status.
Then we will always return the first item of `statuses` here or only
return error status, and this is why in the first picture the commit
status is `Success` but not `Failure`.

https://github.com/go-gitea/gitea/blob/af1ffbcd63569df8646b20c524378f25710f129e/models/git/commit_status.go#L204-L211

Co-authored-by: Giteabot <[email protected]>

Author: yp05327

models/git/commit_status.go

@@ -194,7 +194,7 @@ func (status *CommitStatus) APIURL(ctx context.Context) string {
 // CalcCommitStatus returns commit status state via some status, the commit statues should order by id desc
 func CalcCommitStatus(statuses []*CommitStatus) *CommitStatus {
 	var lastStatus *CommitStatus
-	var state api.CommitStatusState
+	state := api.CommitStatusSuccess
 	for _, status := range statuses {
 		if status.State.NoBetterThan(state) {
 			state = status.State