Fix syntax error

This fixes e65d9c4f. Setting a variable can't end with :
This also fixes the issue with referenced before assignment

src/modules/displaymanager/main.py

@@ -203,10 +203,9 @@ def run():
     root_mount_point = libcalamares.globalstorage.value("rootMountPoint")
     
     if "default_desktop_environment" in libcalamares.job.configuration:
-        entry = libcalamares.job.configuration["default_desktop_environment"]:
+        entry = libcalamares.job.configuration["default_desktop_environment"]
         default_desktop_environment = DesktopEnvironment(entry["executable"], entry["desktop_file"])
-
-    if default_desktop_environment is None:
+    else:
         default_desktop_environment = find_desktop_environment(root_mount_point)
 
     # Setup slim