tests: update self-sigs on our test keys

gpg upstream committed "gpgv: Tweak default options for extra
security." applied on the 1.x and 2.x branches:
http://git.gnupg.org/cgi-bin/gitweb.cgi?p=gnupg.git;a=commit;h=e32c575e0f3704e7563048eea6d26844bdfc494b
This commit includes "[…], but we should validate the key by its self
signature for primary key, and back signature for subkey."

Our testkeys are old and do not really considered best practices in the
last years, so their most recent self-signature is SHA1-only which with
this gpg commit and our testcases defaulting to --weak-digest sha1 are
refused.

So what we do here is just applying some of the recent best practices on
top of our testcase keys.

Gbp-Dch: Ignore