Add prove6 invocation to bin/test-script.sh

This is an unoptimized "do everything" script, but it is enough to
get CI started.

bin/test-script.sh

@@ -10,11 +10,17 @@
 #     podman run -v $PWD:/src -w /src docker.io/rakudo-star:latest sh ./bin/test-script.sh
 #
 set -e
+echo "Installing system dependencies."
 apt-get update -y
 apt-get install -y build-essential
 
+echo "Installing Raku library dependencies."
 zef install --deps-only .
-
 zef install -/precompile-install .
 
+# prove6 is pre-installed in the open source rakudo-star image
+echo "Running tests with prove6."
+prove6 xt/*
+
+echo "Done."