enforce explanation for necessary nolints and fix bugs (#34883)

Follows up https://github.com/go-gitea/gitea/pull/34851

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

services/migrations/migrate.go

@@ -75,11 +75,9 @@ func IsMigrateURLAllowed(remoteURL string, doer *user_model.User) error {
 		return &git.ErrInvalidCloneAddr{Host: u.Host, IsProtocolInvalid: true, IsPermissionDenied: true, IsURLError: true}
 	}
 
-	hostName, _, err := net.SplitHostPort(u.Host)
-	if err != nil {
-		// u.Host can be "host" or "host:port"
-		err = nil //nolint:ineffassign,wastedassign
-		hostName = u.Host
+	hostName, _, errIgnored := net.SplitHostPort(u.Host)
+	if errIgnored != nil {
+		hostName = u.Host // u.Host can be "host" or "host:port"
 	}
 
 	// some users only use proxy, there is no DNS resolver. it's safe to ignore the LookupIP error