locks: expect repo lock, not wlock, when writing to .hg/strip-backup/

There should be no need for a working copy lock when creating (or
reading) bundles in `.hg/strip-backup/` since they don't affect the
working copy.

I noticed this because we have an extension that tries to strip some
revisions while holding only a repo lock. I guess we have no such
cases in core, which seems a bit surprising. Maybe we always take a
wlock at a higher level so the working copy is not updated while the
target commit is being stripped.

Differential Revision: https://phab.mercurial-scm.org/D8666

mercurial/localrepo.py

@@ -1235,8 +1235,9 b' class localrepository(object):'
             if path.startswith(b'cache/'):
                 msg = b'accessing cache with vfs instead of cachevfs: "%s"'
                 repo.ui.develwarn(msg % path, stacklevel=3, config=b"cache-vfs")
-            if path.startswith(b'journal.') or path.startswith(b'undo.'):
-                # journal is covered by 'lock'
+            # path prefixes covered by 'lock'
+            vfs_path_prefixes = (b'journal.', b'undo.', b'strip-backup/')
+            if any(path.startswith(prefix) for prefix in vfs_path_prefixes):
                 if repo._currentlock(repo._lockref) is None:
                     repo.ui.develwarn(
                         b'write with no lock: "%s"' % path,