test-gpg: make sure gpg does not modify the trustdb.gpg file

Tests really should not modify files in the Mercurial working dir
where they ran from! I suspect that trustdb.gpg is now old enough that
GPG thinks it should update it automatically. Suppress that feature
with --no-auto-check-trustdb.

tests/test-gpg.t

@@ -6,7 +6,7 b' Test the GPG extension'
   > gpg=
   > 
   > [gpg]
-  > cmd=gpg --no-permission-warning --no-secmem-warning --homedir $TESTDIR/gpg
+  > cmd=gpg --no-permission-warning --no-secmem-warning --no-auto-check-trustdb --homedir $TESTDIR/gpg
   > EOF
   $ hg init r
   $ cd r
@@ -25,3 +25,7 b' Test the GPG extension'
   $ hg sigcheck 0
   e63c23eaa88a is signed by:
    hgtest
+
+verify that this test has not modified the trustdb.gpg file back in
+the main hg working dir
+  $ hg --cwd $TESTDIR status gpg