Share job workspace with dind for docker compose bind-mounts

docker compose bind-mounts use absolute paths that must be
resolvable by the dind daemon.  Mount the job workspace into
the dind service so it can see the checked-out source tree.

Author: arr2036

.github/workflows/ci-multi-server-tests.yml

@@ -26,8 +26,13 @@ jobs:
           NO_PROXY: "*.networkradius.com,127.0.0.1"
         #  Mount the host's internal CA so dind trusts
         #  docker.internal.networkradius.com for image pulls.
+        #
+        #  Share the job workspace with dind so that docker compose
+        #  bind-mounts (radiusd.conf, env-setup.sh, listener dirs,
+        #  etc.) resolve to real files inside the dind daemon.
         volumes:
           - /usr/local/share/ca-certificates/networkradius.com.crt:/etc/docker/certs.d/docker.internal.networkradius.com/ca.crt:ro
+          - ${{ github.workspace }}:${{ github.workspace }}
 
     env:
       MULTI_SERVER_TEST_LOG: build/tests/multi-server/freeradius-multi-server/multi_server_test.log