mavsdk_tests: fix model name of plane

However, the test does not pass yet, so I'm leaving it commented out.

test/mavsdk_tests/mavsdk_test_runner.py

@@ -23,7 +23,7 @@ test_matrix = [
         "timeout_min": 20,
     },
     # {
-    #     "model": "standard_plane",
+    #     "model": "plane",
     #     "test_filter": "[plane]",
     #     "timeout_min": 25,
     # }