FIX selector = 0 returns all traces in select_traces

[wf-r]

Fix https://github.com/plotly/plotly.py/issues/3639 (selector = 0 in update_traces selects all traces, not only the first one)

Code PR

• [x] I have read through the contributing notes and understand the structure of the package. In particular, if my PR modifies code of plotly.graph_objects, my modifications concern the codegen files and not generated files.
• [x] I have added tests (if submitting a new feature or correcting a bug) or modified existing tests.

[wf-r]

Hmm, I cannot connect the failed test with my changes. Anybody an idea?

[nicolaskruchten]

Thanks!