Fix syntax of test with small timerange

Author: hborchardt

test/image/mocks/zz-gl3d_surface_small_timerange.json

@@ -5,7 +5,7 @@
         "x": [0.1, 0.2],
         "y": [
           "2024-02-03T10:00:00",
-          "2024-02-03T11:00:00",
+          "2024-02-03T11:00:00"
         ],
         "z": [
           [1001, 1002],
@@ -40,4 +40,4 @@
             }
         }
     }
-}
+}