test: add basic deepcopy figure test

Author: FBruzzesi

packages/python/plotly/_plotly_utils/tests/validators/test_fig_deepcopy.py

@@ -0,0 +1,11 @@
+import copy
+import plotly.express as px
+
+
+def test_deepcopy():
+    gapminder = px.data.gapminder()
+    fig = px.line(gapminder, x="year", y="gdpPercap", color="country")
+
+    fig_copy = copy.deepcopy(fig)
+
+    assert fig_copy is not None