test: signature verification check

Author: martgil

FlowCrypt/src/androidTest/assets/messages/mime/signature_verification_cleartext_only_signed.txt

@@ -21,7 +21,7 @@ Content-Transfer-Encoding: 7bit
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA512
 
-It's a cleartext signed message
+It's a tampered signed message
 -----BEGIN PGP SIGNATURE-----
 Version: PGPainless