fix websocket server & add ci test for building it (#4047)

the axum update broke the websocket server, because yerpc still uses a the old 5.9 version.
So I needed to downgrade the dependency until https://github.com/deltachat/yerpc/pull/35 is merged.

I want to retry the kaiOS client experiment, for this I need a working websocket server binary.

.github/workflows/jsonrpc.yml

@@ -35,6 +35,10 @@ jobs:
           npm run test
         env:
           DCC_NEW_TMP_EMAIL: ${{ secrets.DCC_NEW_TMP_EMAIL }}
+      - name: make sure websocket server version still builds
+        run: |
+          cd deltachat-jsonrpc
+          cargo build --bin deltachat-jsonrpc-server --features webserver
       - name: Run linter
         run: |
           cd deltachat-jsonrpc/typescript