chore: clean up tests (#37715)

1. use MockVariableValue as much as possible
2. use wg.Go as much as possible instead of Add/Done
3. simplify global lock's DefaultLocker logic to make it easier to test
4. introduce a general approach for getting external service config in
CI
5. remove unclear & unnecessary "t.Skip"
6. use modern generic syntax for remaining "DecodeJSON" calls
7. clarify test result for "list gitignore templates" and "list
licenses"

tests/integration/api_actions_artifact_v4_test.go

@@ -398,7 +398,7 @@ func TestActionsArtifactV4UploadSingleFileWithChunksOutOfOrder(t *testing.T) {
 				defer test.MockVariableValue(&setting.Actions.ArtifactStorage.AzureBlobConfig.ServeDirect, entry.serveDirect)()
 			default:
 				if entry.serveDirect {
-					t.Skip()
+					t.Skip("for non-serve-direct only")
 				}
 			}
 			// acquire artifact upload url
@@ -529,7 +529,7 @@ func TestActionsArtifactV4DownloadSingle(t *testing.T) {
 				defer test.MockVariableValue(&setting.Actions.ArtifactStorage.MinioConfig.ServeDirect, entry.ServeDirect)()
 			default:
 				if entry.ServeDirect {
-					t.Skip()
+					t.Skip("for non-serve-direct only")
 				}
 			}