Switch to entirely new action for changelog check

Look, let's just be real here: GitHub needs to redo the entire
permission model for GitHub. There is no way to create a secure
combination of the following elements: post comment, edit comment, and
post status check.

If you want to be able to post comments, you have to authorize a token
or app to have full authority to do literally anything that the user can
do on a public repo. Full stop.

If you want to post a status check, you have to give the user write
access to the entire repo, which makes the first issue a problem.

You can't just explicitly make a token that says "only allow this user
to post and edit its own comments" and "allow this user to post status
checks" because write access on the repo implies authority over all
other issues/PRs opened by other people.

Now Cardinal's token is restricted to just status checks, and we're
using a different action.

Thanks a ton for the huge mess Github.

.github/workflows/danger.yml

@@ -4,18 +4,19 @@ on:
   pull_request:
     types: [synchronize, edited, opened, reopened]
 jobs:
-  run:
-    name: Run danger checks
+  build:
+    name: Run changelog check
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v2
-      with:
-        fetch-depth: 100
-        submodules: 'recursive'
-    - name: Install danger
-      run: |
-        sudo gem install danger
-    - name: Run danger
-      env:
-        DANGER_GITHUB_API_TOKEN: ${{ secrets.CARDINAL_PAT_CI_STATUS }}
-      run: danger
+      - uses: actions/checkout@v2
+        with:
+          submodules: 'recursive'
+      - name: Changelog check
+        uses: Zomzog/changelog-checker@564f4aa7a062e7498bd253f616569f02fb024c06
+        with:
+          fileName: CHANGELOG.md
+          noChangelogLabel: Blocked
+          checkNotification: Simple
+        env:
+          GITHUB_TOKEN: ${{ secrets.CARDINAL_PAT_CI_STATUS }}
+