build: Remove nightly release

I have a feeling that it's giving users the feeling they'd be able to get notified of new nightly builds, which doesn't happen. Use GitHub Actions to download nightly builds like before.

.github/workflows/main.yml

@@ -28,14 +28,12 @@ jobs:
           path: build/*/*.zip
       - name: Upload build
         uses: svenstaro/upload-release-action@2.9.0
-        if: github.event_name != 'pull_request'
+        if: github.event_name == 'release'
         with:
           repo_token: ${{ secrets.GITHUB_TOKEN }}
           file: build/*/*.zip
-          tag: ${{ github.event_name == 'release' && github.ref || 'nightly' }}
-          body: ${{ github.event_name != 'release' && github.event.head_commit.message || '' }}
+          tag: ${{ github.ref }}
           file_glob: true
-          prerelease: ${{ github.event_name != 'release' }}
           overwrite: true
 
   analyse-clang: