scm: use dulwich backend when fetching exps during clone/pull (#9023)

refspecs uses pygit2 backend by default, which does not support git credential
helpers. This PR forces to use dulwich backend during clone/pull operations.

dvc/external_repo.py

@@ -253,7 +253,7 @@ def _pull(git: "Git", unshallow: bool = False):
 
     git.fetch(unshallow=unshallow)
     _merge_upstream(git)
-    fetch_all_exps(git, "origin")
+    fetch_all_exps(git, "origin", backends=["dulwich"])
 
 
 def _merge_upstream(git: "Git"):

dvc/repo/experiments/utils.py

@@ -5,6 +5,7 @@ from collections import defaultdict
 from functools import wraps
 from typing import (
     TYPE_CHECKING,
+    Any,
     Callable,
     Dict,
     Generator,
@@ -279,17 +280,15 @@ def check_ref_format(scm: "Git", ref: ExpRefInfo):
         )
 
 
-def fetch_all_exps(scm: "Git", url: str, progress: Optional[Callable] = None):
+def fetch_all_exps(
+    scm: "Git", url: str, progress: Optional[Callable] = None, **kwargs: Any
+):
     refspecs = [
         f"{ref}:{ref}"
-        for ref in iter_remote_refs(scm, url, base=EXPS_NAMESPACE)
+        for ref in iter_remote_refs(scm, url, base=EXPS_NAMESPACE, **kwargs)
         if not (ref.startswith(EXEC_NAMESPACE) or ref in STASHES)
     ]
-    scm.fetch_refspecs(
-        url,
-        refspecs,
-        progress=progress,
-    )
+    scm.fetch_refspecs(url, refspecs, progress=progress, **kwargs)
 
 
 def get_random_exp_name(scm, baseline_rev):

dvc/scm.py

@@ -179,7 +179,7 @@ def clone(url: str, to_path: str, **kwargs):
         try:
             git = Git.clone(url, to_path, progress=pbar.update_git, **kwargs)
             if "shallow_branch" not in kwargs:
-                fetch_all_exps(git, url, progress=pbar.update_git)
+                fetch_all_exps(git, url, progress=pbar.update_git, backends=["dulwich"])
             return git
         except InternalCloneError as exc:
             raise CloneError("SCM error") from exc