CI: replace unsupported upload/download-artifact@v4 with shared host dir

Forgejo does not support @actions/artifact v2 (GHES limitation).
Self-hosted jobs share /tmp/ci-artifacts between jobs.

.forgejo/workflows/release.yml

@@ -20,7 +20,6 @@ jobs:
 
       - name: Decode keystore
         run: echo "${{ secrets.KEYSTORE_B64 }}" | base64 -d > android/keystore/sylda.jks
-        if: env.KEYSTORE_B64 != ''
 
       - name: Write signing.properties
         run: |
@@ -46,12 +45,6 @@ jobs:
           cd release/artifacts
           sha256sum * > checksums.txt
 
-      - name: Upload release artifacts
-        uses: actions/upload-artifact@v4
-        with:
-          name: release
-          path: release/artifacts/*
-
       - name: Create Forgejo release
         uses: https://git.eddydevink.nl/api/packages/eddy/actions/forgejo-release@v1
         with: