tests: treat gpg 'Bad passphrase' as transient under CI load

[ronaldtse]

Summary

• Follow-up to Intermittent gpg-interop CLI test failures: 'Corrupted protection' / 'BAD signature' under parallel CI #2457/tests: re-run whole test on gpg transient failures #2476: the gpg-agent state failure that prints as Corrupted protection on some gpg versions surfaces as Bad passphrase on others - seen failing cli_tests-Compression on the debian-13 leg of cli: verify signatures of side-loadable DLLs on Windows (#2411) #2478 (log: gpg signing failed: Bad passphrase, first occurrence, no code relation to that PR).
• Added to GPG_TRANSIENT_ERRORS so the existing in-call retry + whole-test re-run machinery covers it. Deterministic passphrase failures (genuine regressions) still fail after all attempts - the retry only converts single-shot agent hiccups into passes.

Test plan

• CI green
• No behavior change for deterministic gpg failures (3 attempts then fail)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.46%. Comparing base (cc4b4ea) to head (50dd2af).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2480      +/-   ##
==========================================
- Coverage   85.47%   85.46%   -0.01%     
==========================================
  Files         125      125              
  Lines       22962    22962              
==========================================
- Hits        19626    19625       -1     
- Misses       3336     3337       +1     

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[ronaldtse]

@ni4 one-line test-infra follow-up for your single-approval class, all checks green (only the known fuzzing exceptions): adds Bad passphrase to GPG_TRANSIENT_ERRORS - it's the same gpg-agent state failure as Corrupted protection (#2457), just the wording some gpg versions use (first seen failing cli_tests-Compression on debian-13 yesterday; today the same agent state hit cli_tests-Encryption on a Fedora leg as Corrupted protection). Deterministic passphrase bugs still fail after all retry attempts.

[ni4]

LGTM, thanks! Merging with single approval as CI-only.