Bump slimmer from 18.6.1 to 18.6.2

Bumps [slimmer](https://github.com/alphagov/slimmer) from 18.6.1 to 18.6.2.
- [Changelog](https://github.com/alphagov/slimmer/blob/main/CHANGELOG.md)
- [Commits](alphagov/slimmer@v18.6.1...v18.6.2)

---
updated-dependencies:
- dependency-name: slimmer
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -246,7 +246,7 @@ GEM
     method_source (1.1.0)
     mime-types (3.5.2)
       mime-types-data (~> 3.2015)
-    mime-types-data (3.2024.0820)
+    mime-types-data (3.2024.0903)
     mini_mime (1.1.5)
     mini_portile2 (2.8.7)
     minitest (5.25.1)
@@ -631,7 +631,7 @@ GEM
     simplecov-rcov (0.3.7)
       simplecov (>= 0.4.1)
     simplecov_json_formatter (0.1.4)
-    slimmer (18.6.1)
+    slimmer (18.6.2)
       json
       nokogiri (~> 1.7)
       null_logger