Workaround reflog corruption bug in git 2.48

In git 2.48, there is an issue where using `git update-ref` add a new
entry to the reflog for a branch will cause corrupted reflog entries to
be created for any symbolic refs referencing the updated reference. This
impacts most usage of `git-revise`, as we update the default `HEAD`
reference indirectly due to using `git rev-parse --symbolic-full-name`
to resolve the identity of a branch.

This patch works around this issue in the common case by checking if the
given name directly names a valid ref or symbolic ref, skipping the
`--symbolic-full-name` resolution if it does. This means that HEAD will
be directly updated by `git update-ref`, and receive valid reflog
entries.

This workaround shouldn't negatively impact other git versions, and is
largely an internal change to how symbolic refs are handled by the
odb.Reference type.

See #138 for details.

gitrevise/odb.py

@@ -885,7 +885,20 @@ class Reference(Generic[GitObjT]):  # pylint: disable=unsubscriptable-object
 
     def __init__(self, obj_type: Type[GitObjT], repo: Repository, name: str) -> None:
         self._type = obj_type
-        self.name = repo.git("rev-parse", "--symbolic-full-name", name).decode()
+
+        self.name = name
+        try:
+            # Silently verify that a ref with the name exists and recover if it
+            # doesn't.
+            repo.git("show-ref", "--quiet", "--verify", self.name)
+        except CalledProcessError:
+            # `name` could be a branch name which can be resolved to a ref. Try
+            # to do so with `rev-parse`, and verify that the new name exists.
+            self.name = repo.git(
+                "rev-parse", "--symbolic-full-name", self.name
+            ).decode()
+            repo.git("show-ref", "--verify", self.name)
+
         self.repo = repo
         self.refresh()