Upload jar to release

Author: Shweit

.github/workflows/release.yml

@@ -85,4 +85,12 @@ jobs:
             spigot
             bukkit
           changelog: |
-            See [GitHub Release](${{ github.event.release.html_url }}) for changelog.
+            See [GitHub Release](${{ github.event.release.html_url }}) for changelog.
+
+      - name: Upload Jar to GitHub Release
+        uses: actions/upload-release-asset@v1
+        with:
+          upload_url: ${{ github.event.release.upload_url }}
+          asset_path: ${{ steps.artifact.outputs.jar_path }}
+          asset_name: MinecraftServerAPI-${{ steps.artifact.outputs.version }}.jar
+          asset_content_type: application/java-archive