test: replace aging OpenPGP key used in the test suite

This replaces the old OpenPGPv4 key that is used in the test suite
with a more modern OpenPGPv4 key.  All cryptographic artifacts in the
test suite are updated accordingly.

Having old cryptographic artifacts in the test suite presents a
problem once the old algorithms are rejected by contemporary
implementations.

For reference, this is the old key.

  sec   rsa1024 2011-02-05 [SC]
        5AEAB11F5E33DCE875DDB75B6D92612D94E46381
  uid           [ unknown] Notmuch Test Suite <test_suite@notmuchmail.org> (INSECURE!)
  ssb   rsa1024 2011-02-05 [E]

And this is the new key.  Note that is has the same shape, but uses
Ed25519 and Cv25519 instead of 1024-bit RSA.

  sec   ed25519 2022-09-07 [SC]
        9A3AFE6C60065A148FD4B58A7E6ABE924645CC60
  uid           [ultimate] Notmuch Test Suite (INSECURE!) <test_suite@notmuchmail.org>
  ssb   cv25519 2022-09-07 [E]