They started failing after gnupg: 2.4.0 -> 2.4.1:
T350-crypto: Testing PGP/MIME signature verification and decryption
PASS emacs delivery of signed message via fcc
PASS emacs delivery of signed message via fcc and smtp
PASS signed part content-type indexing
PASS signature verification
PASS detection of modified signed contents
PASS corrupted pgp/mime signature
PASS signature verification without full user ID validity
PASS signature verification with signer key unavailable
FATAL: /build/notmuch-0.37/test/T350-crypto.sh: interrupted by signal 15
[...]
T357-index-decryption: Testing indexing decrypted mail
FATAL: /build/notmuch-0.37/test/T357-index-decryption.sh: interrupted by signal 15
I hope the failures don't signify a real issue.
There's also gnupg22 which would pass these tests,
but it's currently marked as vulnerable (transitively).
1d6af3f762