Allow GPGFinder to work with nonstandard GPG version strings

[sleepdeprecation]

Description of the Change

This changes GPGFinder to allow for nonstandard version strings.

Specifically, I have MacGPG installed instead of upstream GPG, which results in the version string reading gpg (GnuPG/MacGPG2) 2.2.17 instead of the expected gpg (GnuPG) 2.2.17

Checklist

• unit-test added (if change is algorithm)
• functional test added/updated (if change is functional)
• man page updated (if applicable)
• bash completion updated (if applicable)
• documentation updated
• author name in AUTHORS

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I'm not sure if the unchecked items are applicable. A unit test could probably be added, though I'm not entirely sure how other than possibly making a mock binary that responds to --version with the MacGPG version string and adding it to the test-bins.

[codecov]

Codecov Report

Merging #888 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #888      +/-   ##
==========================================
+ Coverage   63.77%   63.79%   +0.02%     
==========================================
  Files          54       54              
  Lines        6673     6674       +1     
==========================================
+ Hits         4256     4258       +2     
  Misses       1890     1890              
+ Partials      527      526       -1

Impacted Files	Coverage Δ
pgp/gnupg_finder.go	68.65% <100%> (+0.47%)	⬆️
deb/remote.go	60.91% <0%> (+0.2%)	⬆️

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[smira]

Thanks, lgtm! 👍