ci: attempt to support non-PR changes

.github/workflows/check.yml

@@ -114,28 +114,31 @@ jobs:
     runs-on: ubuntu-latest
     if: "!contains(github.event.pull_request.title, '[skip ci]')"
     steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 2 # slows down checkout, but we need to compare against the previous commit on push events
+
       - name: Get list of changed files from PR
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         shell: bash
         run: |
-          gh api repos/${{ github.repository }}/pulls/${{ github.event.number }}/files --paginate \
-            | jq '.[] | select(.status != "removed") | .filename' \
-            > "$HOME/changed_files"
+          if [[ "${{ github.event_name }}" == "pull_request" ]]; then
+            gh api repos/${{ github.repository }}/pulls/${{ github.event.number }}/files --paginate \
+              | jq -r '.[] | select(.status != "removed") | .filename' \
+              > "$HOME/changed_files"
+          else
+            git diff --name-only HEAD^ > "$HOME/changed_files"
 
       - name: Print list of changed files
         run: |
           cat "$HOME/changed_files"
 
-      - name: Checkout
-        uses: actions/checkout@v4
-        with:
-          ref: refs/pull/${{ github.event.pull_request.number }}/merge
-
       - name: Install Nix
         uses: DeterminateSystems/nix-installer-action@main
 
-      - name: Checking EditorConfig
+      - name: Checking Editorconfig conformance
         shell: bash
         run: |
           < "$HOME/changed_files" nix-shell -p editorconfig-checker --run 'xargs -r editorconfig-checker -disable-indent-size'