Python API: Fix partial build

`gpu_extras` was always visible

doc/python_api/sphinx_doc_gen.py

@@ -224,6 +224,7 @@ else:
         "bmesh.geometry",
         "bpy.app",
         "bpy.app.handlers",
+        "bpy.app.timers",
         "bpy.app.translations",
         "bpy.context",
         "bpy.data",
@@ -238,6 +239,7 @@ else:
         "gpu.types",
         "gpu.matrix",
         "gpu.select",
+        "gpu_extras",
         "idprop.types",
         "mathutils",
         "mathutils.bvhtree",