CI: LibreSSL QUIC Interop: fix docker context

in the commit haproxy/haproxy@9809928
building docker was switched to URL, but I forgotten to change context.

this is a followup fix.

Author: chipitsine

.github/workflows/quic-interop-libressl.yml

@@ -31,7 +31,7 @@ jobs:
         id: push
         uses: docker/build-push-action@v5
         with:
-          context: haproxy-qns
+          context: https://github.com/haproxytech/haproxy-qns.git
           push: true
           build-args: |
             SSLLIB: LibreSSL