Dockerfile: update containerd binary to v2.0.0-rc.6

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

Dockerfile

@@ -1,7 +1,7 @@
 # syntax=docker/dockerfile-upstream:master
 
 ARG RUNC_VERSION=v1.1.15
-ARG CONTAINERD_VERSION=v1.7.23
+ARG CONTAINERD_VERSION=v2.0.0-rc.6
 # CONTAINERD_ALT_VERSION_16 defines fallback containerd version for integration tests
 ARG CONTAINERD_ALT_VERSION_16=v1.6.36
 ARG REGISTRY_VERSION=v2.8.3
@@ -226,7 +226,11 @@ RUN --mount=target=/root/.cache,type=cache <<EOT
     mv bin/containerd bin/containerd-shim* /out
   else
     CGO_ENABLED=0 make STATIC=1 binaries
-    mv bin/containerd${ext} bin/containerd-shim* /out
+    mv bin/containerd${ext} /out
+    # No shim binary is built for FreeBSD, since containerd v2.0.
+    if ls bin/containerd-shim* >/dev/null 2>&1; then
+      mv bin/containerd-shim* /out
+    fi
   fi
 EOT