Fix inability to delete container registry tags

Because container registry tags can have periods, the addition of the `.json`
format caused ambiguity. Since the tag name regex is greedy, it would attempt
to locate an image named `foo.json` instead of `foo`.

Closes #39260

app/serializers/container_tag_entity.rb

@@ -4,7 +4,7 @@ class ContainerTagEntity < Grape::Entity
   expose :name, :location, :revision, :short_revision, :total_size, :created_at
 
   expose :destroy_path, if: -> (*) { can_destroy? } do |tag|
-    project_registry_repository_tag_path(project, tag.repository, tag.name, format: :json)
+    project_registry_repository_tag_path(project, tag.repository, tag.name)
   end
 
   private

config/routes/project.rb

@@ -281,8 +281,13 @@ constraints(ProjectUrlConstrainer.new) do
 
       namespace :registry do
         resources :repository, only: [] do
-          resources :tags, only: [:index, :destroy],
-                           constraints: { id: Gitlab::Regex.container_registry_tag_regex }
+          # We default to JSON format in the controller to avoid ambiguity.
+          # `latest.json` could either be a request for a tag named `latest`
+          # in JSON format, or a request for tag named `latest.json`.
+          scope format: false do
+            resources :tags, only: [:index, :destroy],
+                             constraints: { id: Gitlab::Regex.container_registry_tag_regex }
+          end
         end
       end