Update test for not mandatory format parameter

Author: pblottiere

tests/src/python/test_qgsserver_wms_getprint.py

@@ -51,7 +51,6 @@ def test_wms_getprint_basic(self):
             "VERSION": "1.1.1",
             "REQUEST": "GetPrint",
             "TEMPLATE": "layoutA4",
-            "FORMAT": "png",
             "map0:EXTENT": "-33626185.498,-13032965.185,33978427.737,16020257.031",
             "map0:LAYERS": "Country,Hello",
             "CRS": "EPSG:3857"