N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.

Error

N: Repository 'https://packaging.gitlab.io/signaling signaling InRelease' changed its 'Origin' value from '' to 'morph027'
N: Repository 'https://packaging.gitlab.io/signaling signaling InRelease' changed its 'Label' value from '' to 'signaling'
N: Repository 'https://packaging.gitlab.io/signaling signaling InRelease' changed its 'Suite' value from '' to 'signaling'

Reason

I have recently added Suite, Origin and Label fields to the repository, which breaks secure apt updates. Unfortunately, there is no way to prevent this.

Solution

As this change is intended, you can unlock updates again by executing apt-get update --allow-releaseinfo-change.