Refactor GitHub Actions workflow to install LaTeX dependencies and build document directly, updating artifact upload step

.github/workflows/main.yml

@@ -36,10 +36,10 @@ jobs:
         run: file ${{ env.PDF_NAME }} || grep -q ' PDF '
 
       - name: Release PDF artifact
+        if: github.event_name == 'push' && github.ref == 'refs/heads/main'
         uses: softprops/action-gh-release@v2
         with:
           files: ${{ env.PDF_NAME }}
-          #token: ${{ secrets.GITHUB_TOKEN }}
           tag_name: latest
           body: |
-            PDF document built from LaTeX source.
+            PDF document built from latest LaTeX source.