Add ubuntu-24.04 label to defaults. (#724)

Simple change to include ubuntu-24.04 in the default list.  While ubuntu-latest already points to the same image (at this time) it is appropriate to have it by version as well.

Co-authored-by: techknowlogick <techknowlogick@gitea.com>
Reviewed-on: https://gitea.com/gitea/act_runner/pulls/724
Co-authored-by: telackey <telackey@noreply.gitea.com>
Co-committed-by: telackey <telackey@noreply.gitea.com>

internal/app/cmd/register.go

@@ -93,8 +93,8 @@ const (
 
 var defaultLabels = []string{
 	"ubuntu-latest:docker://docker.gitea.com/runner-images:ubuntu-latest",
+	"ubuntu-24.04:docker://docker.gitea.com/runner-images:ubuntu-24.04",
 	"ubuntu-22.04:docker://docker.gitea.com/runner-images:ubuntu-22.04",
-	"ubuntu-20.04:docker://docker.gitea.com/runner-images:ubuntu-20.04",
 }
 
 type registerInputs struct {