Fix test cases by reducing the severity of the bgl error message to warning.

source/blender/python/generic/bgl.c

@@ -2644,7 +2644,7 @@ PyObject *BPyInit_bgl(void)
   }
 
   if (GPU_backend_get_type() != GPU_BACKEND_OPENGL) {
-    CLOG_ERROR(&LOG,
+    CLOG_WARN(&LOG,
               "'bgl' imported without an OpenGL backend. Please update your add-ons to use the "
               "'gpu' module. In Blender 3.7 'bgl' will be removed.");
   }