tests: update the detailed exit codes in test-phabricator.t

I'm guessing this has slipped through because most people don't have the
necessary `pytest-vcr` package installed.

Differential Revision: https://phab.mercurial-scm.org/D10297

tests/test-phabricator.t

@@ -48,7 +48,7 b" Missing arguments don't crash, and may p"
   options:
   
   (use 'hg debugcallconduit -h' to show more help)
-  [255]
+  [10]
   $ hg phabread
   abort: empty DREVSPEC set
   [255]