I just ran into the same problem and solved it manually by creating the secring.gpg file by running the following terminal command:
gpg --keyring secring.gpg --export-secret-key XXXXXXXX > secring.gpg
You must replace XXXXXXXX with the identifier of the key you want to use. You can list all available keys using the gpg --list-key command.
Edit: I forgot to mention that I use Linux.
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