gha: nydus: Actually install kata when install-kata is called

We've been simply doing nothing whenever `install-kata` was called, and
that was the intent when we added the placeholder calls.

Now, let's install kata, as expected. :-)

Signed-off-by: Fabiano Fidêncio <fabiano.fidencio@intel.com>
(cherry picked from commit d2b3b67)

tests/integration/nydus/gha-run.sh

@@ -29,7 +29,7 @@ function main() {
 	action="${1:-}"
 	case "${action}" in
 		install-dependencies) install_dependencies ;;
-		install-kata) return 0 ;;
+		install-kata) install_kata ;;
 		run) run ;;
 		*) >&2 die "Invalid argument" ;;
 	esac