project: disable auto-gc for depth=1 in git config

During sync, `git checkout` can trigger fetch for missing objects in
partial clones. This internal fetch can trigger `git maintenance` or
`git gc` and cause delays during the local checkout phase. Set
maintenance.auto to false and gc.auto to 0 in during `_InitRemote` if
`depth=1` to ensure that implicit fetches spawned by git skip GC.

Bug: 379111283
Change-Id: I6b22a4867f29b6e9598746cb752820a84dc2aeb6
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/540681
Reviewed-by: Mike Frysinger <vapier@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>

project.py

@@ -3316,6 +3316,15 @@ class Project:
                 remote.ResetFetch(mirror=True)
             remote.Save()
 
+        # Disable auto-gc for depth=1 to prevent hangs during lazy fetches
+        # inside git checkout for partial clones.
+        effective_depth = (
+            self.clone_depth or self.manifest.manifestProject.depth
+        )
+        if effective_depth == 1:
+            self.config.SetBoolean("maintenance.auto", False)
+            self.config.SetInt("gc.auto", 0)
+
     def _InitMRef(self):
         """Initialize the pseudo m/<manifest branch> ref."""
         if self.manifest.branch: