Fix armored output having incorrect label

Signed-off-by: Wiktor Kwapisiewicz <[email protected]>

README.md

@@ -120,6 +120,7 @@ from pysequoia import sign
 s = Cert.from_file("signing-key.asc")
 signed = sign(s.secrets.signer(), "data to be signed".encode("utf8"))
 print(f"Signed data: {signed}")
+assert "PGP MESSAGE" in str(signed)
 ```
 
 ## Certificates

src/sign.rs

@@ -15,16 +15,10 @@ pub fn sign(signer: PySigner, bytes: &[u8]) -> PyResult<Cow<'static, [u8]>> {
     let mut sink = vec![];
     {
         let message = Message::new(&mut sink);
-
-        let message = Armorer::new(message)
-            .kind(openpgp::armor::Kind::Signature)
-            .build()?;
+        let message = Armorer::new(message).build()?;
         let message = Signer::new(message, signer).build()?;
-
         let mut message = LiteralWriter::new(message).build()?;
-
         message.write_all(bytes)?;
-
         message.finalize()?;
     }