tests: fix formatting test after move of black config

Differential Revision: https://phab.mercurial-scm.org/D7102

tests/test-check-format.t

@@ -3,5 +3,5 b''
 (this should use the actual black as soon as possible)
 
   $ cd $RUNTESTDIR/..
-  $ python3 contrib/grey.py -S --quiet --check --diff `hg files 'set:**.py - hgext/fsmonitor/pywatchman/** - mercurial/thirdparty/** - "contrib/python-zstandard/**" - contrib/grey.py'`
+  $ python3 contrib/grey.py --config=black.toml --check --diff `hg files 'set:**.py - hgext/fsmonitor/pywatchman/** - mercurial/thirdparty/** - "contrib/python-zstandard/**" - contrib/grey.py'`