Fix disabling of Kroki optional formats

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/49304 added
optional Kroki formats, but these were not actually disabled by default.

changelogs/unreleased/sh-fix-kroki-format-filtering.yml

+---
+title: Fix disabling of Kroki optional formats
+merge_request: 55665
+author:
+type: fixed

lib/gitlab/kroki.rb

@@ -31,9 +31,6 @@ module Gitlab
                           DIAGRAMS_FORMATS
                         end
 
-      # No additional diagram formats
-      return diagram_formats unless current_settings.kroki_formats.present?
-
       # Diagrams that require a companion container must be explicitly enabled from the settings
       diagram_formats.select do |diagram_type|
         current_settings.kroki_format_supported?(diagram_type)

spec/lib/gitlab/kroki_spec.rb

+# frozen_string_literal: true
+require 'spec_helper'
+
+RSpec.describe Gitlab::Kroki do
+  using RSpec::Parameterized::TableSyntax
+
+  describe '.formats' do
+    def default_formats
+      %w[bytefield c4plantuml ditaa erd graphviz nomnoml plantuml svgbob umlet vega vegalite wavedrow].freeze
+    end
+
+    subject { described_class.formats(Gitlab::CurrentSettings) }
+
+    where(:enabled_formats, :expected_formats) do
+      ''           | default_formats
+      'blockdiag'  | default_formats + %w[actdiag blockdiag nwdiag packetdiag rackdiag seqdiag]
+      'bpmn'       | default_formats + %w[bpmn]
+      'excalidraw' | default_formats + %w[excalidraw]
+    end
+
+    with_them do
+      before do
+        kroki_formats =
+          if enabled_formats.present?
+            { enabled_formats => true }
+          else
+            {}
+          end
+
+        stub_application_setting(kroki_enabled: true, kroki_url: "http://localhost:8000", kroki_formats: kroki_formats)
+      end
+
+      it 'returns the expected formats' do
+        expect(subject).to match_array(expected_formats)
+      end
+    end
+  end
+end