Add AUR update workflow (#7715)

Port the update workflow from
https://github.com/Thyrum/aur-packages/blob/master/.github/workflows/unciv-bin.yml
to the Unciv github repository.

This does require adding some secrets to the repository and I don't know
how I would do this.

.github/workflows/buildAndDeploy.yml

@@ -192,6 +192,32 @@ jobs:
             ${{ env.RELEASE_BODY }}
 
 
+      - name: Get AUR PKGBUILD
+        if: github.event_name == 'push' && contains(github.ref, 'ref/tags/')
+        continue-on-error: true
+        run: |
+          curl --silent --output PKGBUILD 'https://aur.archlinux.org/cgit/aur.git/plain/PKGBUILD?h=unciv-bin'
+          sed -E -e "s#(_pkgver=).*#\1${{steps.tag.outputs.tag}}#" -e "s#(pkgrel=).*#\10#" -i PKGBUILD
+
+      - name: Publish AUR package
+        if: github.event_name == 'push' && contains(github.ref, 'ref/tags/')
+        continue-on-error: true
+        uses: Thyrum/github-actions-deploy-aur@master
+        with:
+          pkgname: unciv-bin
+          pkgbuild: ./PKGBUILD
+          commit_username: ${{ secrets.AUR_COMMIT_USERNAME }}
+          commit_email: ${{ secrets.AUR_COMMIT_EMAIL }}
+          ssh_private_key: ${{ secrets.AUR_SSH_PRIVATE_KEY }}
+          commit_message: |
+            Update to ${{steps.tag.outputs.tag}}
+
+            ${{ env.RELEASE_BODY }}
+          ssh_keyscan_types: rsa,dsa,ecdsa,ed25519
+          updpkgsums: true
+          allow_empty_commits: false
+
+
       - name: Post announcement on Discord
         continue-on-error: true
         ## On patch releases, don't notify Discord