test-gpg: replace 825565136235 by md5sum check

The call to 'hg identify' would have needed '--cwd "$TESTDIR' to make it work
anyway, but by using a checksum this test can work outside a repository.

tests/test-gpg.t

@@ -1,10 +1,6 b''
 Test the GPG extension
 
   $ "$TESTDIR/hghave" gpg || exit 80
-  $ if ! hg identify -q > /dev/null; then
-  >     echo "skipped: not a Mercurial working dir" >&2
-  >     exit 80
-  > fi
   $ cat <<EOF >> $HGRCPATH
   > [extensions]
   > gpg=
@@ -32,4 +28,5 b' Test the GPG extension'
 
 verify that this test has not modified the trustdb.gpg file back in
 the main hg working dir
-  $ hg --cwd $TESTDIR status gpg
+  $ "$TESTDIR/md5sum.py" "$TESTDIR/gpg/trustdb.gpg"
+  f6b9c78c65fa9536e7512bb2ceb338ae  */gpg/trustdb.gpg (glob)