Fix detect-tests CI job

The detect-tests job is failing in
https://gitlab.com/gitlab-renovate-forks/gitlab/-/jobs/6326977771
because `ruby:3.1-slim` doesn't come with `gcc` and `make`, which is
needed to build native extensions. `activesupport` depends on `i18n`,
which depends on `racc`. `racc` has a native extension.

.gitlab/ci/setup.gitlab-ci.yml

@@ -132,7 +132,7 @@ detect-tests:
   variables:
     RSPEC_TESTS_MAPPING_ENABLED: "true"
   before_script:
-    - apt-get update && apt-get install -y curl  # Not present in ruby-slim, so we add it manually
+    - apt-get update && apt-get install -y curl make gcc # Not present in ruby-slim, so we add it manually
   script:
     - source ./scripts/utils.sh
     - source ./scripts/rspec_helpers.sh