Revert govuk_publishing_components major version bump

Despite the tests passing in #1439, the deployment failed
in https://github.com/alphagov/contacts-admin/actions/runs/10166486149
with:

```
```

Reverting so that deployment works again as normal, and we can
investigate bumping govuk_publishing_components again later.

Gemfile

@@ -20,7 +20,7 @@ gem "gds-sso"
 gem "govspeak"
 gem "govuk_admin_template"
 gem "govuk_app_config"
-gem "govuk_publishing_components"
+gem "govuk_publishing_components", "39.2.5"
 gem "plek"
 
 # assets

Gemfile.lock

@@ -216,7 +216,7 @@ GEM
     govuk_personalisation (1.0.0)
       plek (>= 1.9.0)
       rails (>= 6, < 8)
-    govuk_publishing_components (43.1.0)
+    govuk_publishing_components (39.2.5)
       govuk_app_config
       govuk_personalisation (>= 0.7.0)
       kramdown
@@ -749,7 +749,7 @@ DEPENDENCIES
   govspeak
   govuk_admin_template
   govuk_app_config
-  govuk_publishing_components
+  govuk_publishing_components (= 39.2.5)
   govuk_schemas
   json-schema
   mlanett-redis-lock