hghave: update dirstate-v2 format config option

It wasn't kept in sync with the new change in format name.

Differential Revision: https://phab.mercurial-scm.org/D11744

tests/hghave.py

@@ -1061,7 +1061,7 b' def has_repofncache():'
 def has_dirstate_v2():
     # Keep this logic in sync with `newreporequirements()` in `mercurial/localrepo.py`
     return has_rust() and matchoutput(
-        'hg config format.exp-dirstate-v2', b'(?i)1|yes|true|on|always'
+        'hg config format.exp-rc-dirstate-v2', b'(?i)1|yes|true|on|always'
     )