Use tkuschel/gitea-upload-artifact@v7

The official action considers a runner on a custom domain = GHES and
fails to run.

Signed-off-by: Markus Birth <markus@birth-online.de>

.github/workflows/build.yml

@@ -35,7 +35,7 @@ jobs:
           sdk-channel: ${{ matrix.sdk-channel }}
           sdk-index-url: ${{ matrix.sdk-index.url }}
       - name: Upload app artifacts
-        uses: actions/upload-artifact@v3
+        uses: tkuschel/gitea-upload-artifact@v7
         with:
           # See ufbt action docs for other output variables
           name: uk_mbirth_sonicare-${{ steps.build-app.outputs.suffix }}.fap