fix: get_metadata deprecated since traitlets 4.1

[ManonMarchand]

Hello,

This is a very tiny PR, but I get a deprecation warning raised by this line from the traitlets library when using a custom ipywidget:

https://github.com/ipython/traitlets/blob/cb672eb5ba235fdfee6407bd7f1b1985de934e7c/traitlets/traitlets.py#L833

Here is a fix that should remove it?

Edit: I explicitly allow anyone to edit anything I might have done wrong, I have no idea why the tests are failing

[github-actions]

👈 Launch a binder notebook on branch ManonMarchand/ipywidgets/fix-get_metadata

[dangotbanned]

@ManonMarchand could you push this again please?

I can try to help with CI failures, but the original logs aren't visible anymore.

Arrived here after planning to submit an identical PR for vega/altair#3234

[ManonMarchand]

Sure, also rebased on main in case the ci failure wasn't due to the tiny fix

[dangotbanned]

@ManonMarchand looking at the last 4 merged commits, I don't think you should expect anything other than the last 4 tests passing

I've tried using that auto binder link #3894 (comment)
No idea what the expectation there is, but it spent 45 mins building and then printed "Service Unavailable".

---

I think a maintainer will just need to merge as-is.
The failures are already on main and seems very unlikely to me that your change has anything to do with it.

There is also #3932 which seems to be passing CI, but is yet to be reviewed

[martinRenou]

I will try a patch release very soon-ish with this and #3932, thanks @ManonMarchand !

[martinRenou]

Thanks!