Using a workaround that validates passphrase for a secret key.
With GnuPG 2.2.23 and GpgME 1.1.15, a secret key can be exported when the right
passphrase is provided. With a bad passphrase, application crashes.
See https://dev.gnupg.org/T5151
Application may validate a passphrase before invoking engine. Until it is
hopefully fixed in upstream and available in mainstream.
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