statichttprepo: use LockUnavailable() instead of Abort() for lock (API)

If we try to get a lock on statichttprepo, we get `error.Abort()` instead of
subclass of `error.LockError()`. The callers which catches `error.LockError`
fails to catch this case as the correct error is not raised.

Raising `error.LockUnavaible()` is same as what is done for wlock also.

mercurial/statichttprepo.py

@@ -238,7 +238,12 b' class statichttprepository('
         )
 
     def lock(self, wait=True):
-        raise error.Abort(_(b'cannot lock static-http repository'))
+        raise error.LockUnavailable(
+            0,
+            _(b'lock not available'),
+            b'lock',
+            _(b'cannot lock static-http repository'),
+        )
 
     def _writecaches(self):
         pass  # statichttprepository are read only