Fix AM)-signing script after changes in jwt

jwt.encode() now returns string type.

Reference:
- https://pyjwt.readthedocs.io/en/stable/changelog.html#improve-typings

dist/chromium/publish-beta.py

@@ -2,7 +2,6 @@
 
 import datetime
 import json
-import jwt
 import os
 import re
 import requests

dist/firefox/publish-signed-beta.py

@@ -190,7 +190,7 @@ def get_jwt_auth():
         'iat': datetime.datetime.utcnow(),
         'exp': datetime.datetime.utcnow() + datetime.timedelta(seconds=15),
     }
-    return 'JWT ' + jwt.encode(jwt_payload, amo_secret).decode()
+    return 'JWT ' + jwt.encode(jwt_payload, amo_secret)
 
 print('Ask AMO to sign self-hosted xpi package...')
 with open(unsigned_xpi_filepath, 'rb') as f:

dist/mv3/publish-beta.py

@@ -2,7 +2,6 @@
 
 import datetime
 import json
-import jwt
 import os
 import re
 import requests