Test Suite: clean up interactions with gpg

[dkg]

This series cleans up a series of minor quibbles with the way that the RNP test suite interacts with GnuPG.

A future GnuPG may choose responsible cryptographic primitives as a baseline, and decline signatures from or encrypting to 1024-bit RSA, so this series also moves all the tests that expected 1024-bit RSA interoperability to testing the ECC sample key in keyring 5.

GnuPG can also be built without some weaker/deprecated algorithms (e.g., El Gamal and IDEA), so this cleanup skips over some tests for those algorithms if gpg --version doesn't indicate support for them.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 85.46%. Comparing base (bf89f0b) to head (f934805).

Additional details and impacted files

@@             Coverage Diff              @@
##           release/0.x    #2367   +/-   ##
============================================
  Coverage        85.46%   85.46%           
============================================
  Files              126      126           
  Lines            22710    22712    +2     
============================================
+ Hits             19408    19410    +2     
  Misses            3302     3302           

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