add workflow for updating AUR package (#6)

.github/workflows/release.yml

@@ -26,3 +26,17 @@ jobs:
         with:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           RELEASE: true
+
+      - name: Update AUR package
+        if: ${{ matrix.os == 'ubuntu-latest' }}
+        run: |
+          sudo apt install makepkg
+
+          echo $SSH_KEY > ~/.ssh/aur
+          echo $SSH_PUB_KEY > ~/.ssh/aur.pub
+          export GIT_SSH_COMMAND="ssh -i ~/.ssh/aur"
+
+          ./scripts/aur_bump.sh
+        with:
+          SSH_KEY: ${{ secrets.AUR_SSH_KEY }}
+          SSH_PUB_KEY: ${{ secrets.AUR_SSH_PUB_KEY }}