tests/test-gpg.out

tests: fix bashism to load helpers.sh

`source` isn't available at POSIX sh.

adding foo
% no signatures
% hg sign 0
Signing 0:e63c23eaa88a
% hg sigs
hgtest                             0:e63c23eaa88ae77967edcf4ea194d31167c478b0
% hg sigcheck 0
e63c23eaa88a is signed by:
 hgtest