Fix label fields on video editing

[Rahmon]

Description of the Change

The field label is not sent on the form submit when a video is updated. This PR fixes that.

Alternate Designs

Benefits

The user can add/remove labels to a video.

Possible Drawbacks

Verification Process

1. Edit a video and add/remove labels
2. Save the video
3. Refresh the page and check if the value for the label is correct

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry

Fixed label fields on video editing.