fix(ci): Remove automatic assignment of the `C-trivial` label

[upbqdn]

Motivation

The github-actions bot often assigns the C-trivial label to PRs where it shouldn't be. Manually removing the label doesn't help as the bot adds the label back on when the PR is updated.

We use this label to decide what PRs should be present in the release changelog, and having the label assigned to the wrong PRs wastes the release manager's time, and the time of release reviewers.