test compatibility with v5 OpenPGP keys?

[tomholub]

  public static fingerprintToLongid = (fingerprint: string) => {
    if (fingerprint.length === 40) { // pgp keys
      return fingerprint.substr(-16).toUpperCase();
    }
    throw new Error(`Unexpected fingerprint format (len: ${fingerprint.length}): "${fingerprint}"`);
  }

Actually this is ok, however this will not work for v5 OpenPGP keys which use longer fingerprints. I'll file a separate issue.

Originally posted by @tomholub in #3575 (comment)

[tomholub]

May also need to upgrade to OpenPGP.js v5 first #3324