H5P Upload widget PHP notices

Issue exists in D11 as well. Can be tested if based off of https://www.drupal.org/project/h5p/issues/3542700 🐛 Error when uploading an .h5p file through upload form widget Active . (Otherwise H5P Upload field widget has blocking errors for reproduction.)

I've confirmed this does resolve the warning, when paired with 3542700.

The IS references Drupal 9.4. I updated to reference D11

This looks good. I've tested:
- before and after the fix
- on a D10 and D11 site
Everything works as expected and the fix seems reasonable. Marking RTBC.

Thanks! Merged and marking as fixed.

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