Bump Fuchsia (includes building tests)

This includes a change to the upstream build_fuchsia_from_rust_ci script
that builds a minimal set of tests, to improve coverage on this builder.

Author: tmandry

src/ci/docker/host-x86_64/x86_64-gnu-integration/build-fuchsia.sh

@@ -5,7 +5,7 @@
 
 set -euf -o pipefail
 
-INTEGRATION_SHA=66793c4894bf6204579bbee3b79956335f31c768
+INTEGRATION_SHA=56310bca298872ffb5ea02e665956d9b6dc41171
 PICK_REFS=()
 
 checkout=fuchsia