python3: encode oidc authn test claims (#32452)

tests/test_auth_oidc.py

@@ -546,7 +546,7 @@ def test_required_keys(db, oidc_provider, header, signature, caplog):
         'iat': 1311280970,
         'exp': 1311281970, # Missing 'aud' and 'nonce' required claims
         'extra_stuff': 'hi there', # Wrong claim
-    }))
+    }).encode('ascii'))
 
     with pytest.raises(IDTokenError):
         with utils.check_log(caplog, 'missing field'):