Improve test output regexes for better perf and Go 1.20 support

[refi64]

From the first commit:

The current regex runs in exponential time, which massively impacts the
runtime of the test suite, taking several seconds (~4s on my system)
just to perform a single match. By replacing the mix of re.findall + the
initial capture group with re.search + some string slicing, the time
spent matching the regex becomes nearly instant, e.g.:

    $ make system-test TESTS='Config*'

goes from taking ~10s to ~1.5s.

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

[codecov[bot]]

Codecov Report

Merging #1220 (88f1409) into master (18203c6) will increase coverage by 0.01%. Report is 5 commits behind head on master. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1220      +/-   ##
==========================================
+ Coverage   65.95%   65.96%   +0.01%     
==========================================
  Files         143      143              
  Lines       16192    16188       -4     
==========================================
  Hits        10679    10679              
+ Misses       4760     4756       -4     
  Partials      753      753              

see 2 files with indirect coverage changes

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[reglim]

LGTM, @randombenj what do you think?

Also, would you mind adding your name to the AUTHOR file?

[refi64]

@reglim added!