lfs: take lock before writing requirements

With `share-safe`, we will also write file in the store, so we take the store
lock before writing requirements.

Differential Revision: https://phab.mercurial-scm.org/D11991

hgext/lfs/__init__.py

@@ -257,6 +257,7 b' def _reposetup(ui, repo):'
     if b'lfs' not in repo.requirements:
 
         def checkrequireslfs(ui, repo, **kwargs):
+            with repo.lock():
             if b'lfs' in repo.requirements:
                 return 0
 
@@ -269,7 +270,9 b' def _reposetup(ui, repo):'
             for ctx in s:
                 # TODO: is there a way to just walk the files in the commit?
                 if any(
-                    ctx[f].islfs() for f in ctx.files() if f in ctx and match(f)
+                        ctx[f].islfs()
+                        for f in ctx.files()
+                        if f in ctx and match(f)
                 ):
                     repo.requirements.add(b'lfs')
                     repo.features.add(repository.REPO_FEATURE_LFS)