[fix] github action opens PR instead of merging into main (#86)

* [fix] github action opens PR instead of merging into main

* prevent new PR being made after mergining in the new version of the textbook

.github/workflows/generate-pdf.yml

@@ -140,13 +140,25 @@ jobs:
           name: textbook-full
           path: textbook_full.pdf
 
-      - name: Commit and push changes only on push
-        if: github.event_name == 'push'
+      - name: Commit changes to a new branch
+        if: github.event_name == 'push' && !contains(github.event.head_commit.message, 'Update PDF of textbook')
         run: |
           git config --local user.email "github-actions[bot]@users.noreply.github.com"
           git config --local user.name "GitHub Actions"
+          git checkout -b update-textbook-full-pdf-$(date +%s)
           git add textbook_full.pdf
-          git commit -m "Update full PDF of textbook on site"
-          git push
+          git commit -m "Update PDF of textbook on site after a merge to main"
+          git push origin HEAD
         env:
-          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Create a Pull Request
+        if: github.event_name == 'push' && !contains(github.event.head_commit.message, 'Update PDF of textbook')
+        uses: peter-evans/create-pull-request@v5
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          commit-message: "Update PDF of textbook on site"
+          branch: update-textbook-full-pdf-$(date +%s)
+          title: "Update full PDF of textbook"
+          body: "This PR updates the full PDF of the textbook."
+          base: main