Switch release signing to RSA-2048/SHA-256 for openssl compatibility

.github/workflows/release.yml

@@ -104,14 +104,14 @@ jobs:
         working-directory: artifacts
         run: sha256sum * > SHA256SUMS.txt
 
-      - name: sign the checksums (Ed25519)
+      - name: sign the checksums (RSA-2048/SHA-256)
         env:
           KEY: ${{ secrets.SCIMESH_SIGNING_KEY }}
         working-directory: artifacts
         run: |
           if [ -n "$KEY" ]; then
             printf '%s\n' "$KEY" > /tmp/scimesh-sign-key.pem
-            openssl dgst -sign /tmp/scimesh-sign-key.pem \
+            openssl dgst -sha256 -sign /tmp/scimesh-sign-key.pem \
               -out SHA256SUMS.txt.sig SHA256SUMS.txt
             echo "signed SHA256SUMS.txt"
           else