The previous logic using 'file | grep PGP' was inverted — both
ASCII-armored and binary GPG keys matched the pattern, causing
ASCII-armored keys to be copied directly instead of being
dearmored. This resulted in APT failing with NO_PUBKEY errors
on Debian 12 (bookworm).
Use 'grep BEGIN PGP' to reliably detect ASCII-armored keys and
dearmor them, otherwise copy binary keys directly.