Add a typst-package-check step to CI

Author: elegaanz

.github/workflows/test_pr.yml

@@ -49,3 +49,25 @@ jobs:
 
       - name: Test packaging
         run: bundler/target/release/bundler
+
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+    steps:
+      - name: Count how many commits need to be fetched
+        id: base-depth
+        run: echo "base-depth=$(expr ${{ github.event.pull_request.commits }} + 1)" >> $GITHUB_OUTPUT
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: ${{ steps.base-depth.outputs.base-depth }}
+      - name: Fetch necessary Git objects
+        run: |
+          merge_sha=$(/usr/bin/git log -1 --format=%H)
+          git fetch origin ${{ github.base_ref }}
+          git checkout ${{ github.base_ref }}
+          git checkout $merge_sha
+      - uses: typst/[email protected]
+        with:
+          installation-id: ${{ secrets.GH_INSTALLATION_ID }}
+          app-id: ${{ secrets.GH_APP_ID }}
+          private-key: ${{ secrets.GH_PRIVATE_KEY }}