tests: ignore possible diagnostics from gpg 2.2 stable

tests: ignore possible diagnostics from gpg 2.2

Differential Revision: https://phab.mercurial-scm.org/D8672

--- a/tests/test-gpg.t	Wed Jul 01 23:30:47 2020 +0530
+++ b/tests/test-gpg.t	Mon Jun 29 16:36:53 2020 +0200
@@ -35,6 +35,7 @@
   $ hg sigs
 
   $ HGEDITOR=cat hg sign -e 0
+  gpg: error retrieving key fingerprint from card: Invalid name (?)
   signing 0:e63c23eaa88a
   Added signature for changeset e63c23eaa88a