Refactor git command stdio pipe (#36422)

Most potential deadlock problems should have been fixed, and new code is
unlikely to cause new problems with the new design.

Also raise the minimum Git version required to 2.6.0 (released in 2015)

modules/repository/repo.go

@@ -62,7 +62,9 @@ func StoreMissingLfsObjectsInRepository(ctx context.Context, repo *repo_model.Re
 
 	pointerChan := make(chan lfs.PointerBlob)
 	errChan := make(chan error, 1)
-	go lfs.SearchPointerBlobs(ctx, gitRepo, pointerChan, errChan)
+	go func() {
+		errChan <- lfs.SearchPointerBlobs(ctx, gitRepo, pointerChan)
+	}()
 
 	downloadObjects := func(pointers []lfs.Pointer) error {
 		err := lfsClient.Download(ctx, pointers, func(p lfs.Pointer, content io.ReadCloser, objectError error) error {
@@ -150,13 +152,12 @@ func StoreMissingLfsObjectsInRepository(ctx context.Context, repo *repo_model.Re
 		}
 	}
 
-	err, has := <-errChan
-	if has {
+	err := <-errChan
+	if err != nil {
 		log.Error("Repo[%-v]: Error enumerating LFS objects for repository: %v", repo, err)
-		return err
 	}
 
-	return nil
+	return err
 }
 
 // shortRelease to reduce load memory, this struct can replace repo_model.Release