Stop verifying the CHANGELOG on every PR

It's a real pain to keep it up-to-date. Way easier
to generate it with a script before release.

.github/workflows/verify.yml

@@ -1,19 +0,0 @@
-name: Verify
-on:
-  pull_request:
-    branches:
-      - master
-jobs:
-  changelog:
-    runs-on: ubuntu-20.04
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        fetch-depth: 0
-    - name: Check `CHANGELOG.md` has changes
-      run: |
-        ! git diff --exit-code origin/master HEAD -- CHANGELOG.md
-    - name: Check `CHANGELOG.md` thanks the PR author
-      if: ${{ github.event.pull_request.user.login != 'hecrj' }}
-      run: |
-        sed -n '/## \[Unreleased\]/,/^## /p' CHANGELOG.md | sed -n '/Many thanks to.../,//p' | grep '@${{ github.event.pull_request.user.login }}'