ci: Clean up potentially leftover state in case job was cancelled

Happened in https://buildkite.com/materialize/nightly/builds/10992#0194ae51-f610-4440-84f7-84fb30f17361

The usual cleanup logic can't be run even though it's in a `finally`
block in our Python test code. The `pre-exit` hook is still being run.

ci/plugins/mzcompose/hooks/pre-exit

@@ -145,3 +145,7 @@ ci_unimportant_heading ":docker: Cleaning up after mzcompose"
 run kill || true
 run rm --force -v
 run down --volumes
+
+ci_unimportant_heading "terraform: Destroying leftover state in case job was cancelled or timed out..."
+bin/ci-builder run stable terraform -chdir=test/terraform/aws destroy || true
+bin/ci-builder run stable terraform -chdir=test/terraform/gcp destroy || true