Bump slimmer from 18.1.0 to 18.2.0

Bumps [slimmer](https://github.com/alphagov/slimmer) from 18.1.0 to 18.2.0.
- [Changelog](https://github.com/alphagov/slimmer/blob/main/CHANGELOG.md)
- [Commits](alphagov/slimmer@v18.1.0...v18.2.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile.lock

@@ -108,8 +108,7 @@ GEM
     date (3.3.4)
     debug_inspector (1.1.0)
     docile (1.4.0)
-    domain_name (0.5.20190701)
-      unf (>= 0.0.5, < 1.0.0)
+    domain_name (0.6.20231109)
     erubi (1.12.0)
     execjs (2.8.1)
     faker (3.2.2)
@@ -187,7 +186,7 @@ GEM
       rails-i18n
       rainbow (>= 2.2.2, < 4.0)
       terminal-table (>= 1.5.1)
-    json (2.6.3)
+    json (2.7.1)
     json-schema (4.1.1)
       addressable (>= 2.8)
     kramdown (2.4.0)
@@ -210,7 +209,7 @@ GEM
     method_source (1.0.0)
     mime-types (3.5.1)
       mime-types-data (~> 3.2015)
-    mime-types-data (3.2023.0808)
+    mime-types-data (3.2023.1205)
     mini_mime (1.1.5)
     mini_portile2 (2.8.5)
     minitest (5.20.0)
@@ -570,7 +569,7 @@ GEM
       simplecov_json_formatter (~> 0.1)
     simplecov-html (0.12.3)
     simplecov_json_formatter (0.1.4)
-    slimmer (18.1.0)
+    slimmer (18.2.0)
       json
       nokogiri (~> 1.7)
       null_logger
@@ -596,9 +595,6 @@ GEM
       concurrent-ruby (~> 1.0)
     uglifier (4.2.0)
       execjs (>= 0.3.0, < 3)
-    unf (0.1.4)
-      unf_ext
-    unf_ext (0.0.8.2)
     unicode-display_width (2.4.2)
     webmock (3.19.1)
       addressable (>= 2.8.0)