Enable more frozen string in app/models/**/*.rb

Partially addresses #47424.

app/models/concerns/expirable.rb

+# frozen_string_literal: true
+
 module Expirable
   extend ActiveSupport::Concern

app/models/concerns/fast_destroy_all.rb

+# frozen_string_literal: true
+
 ##
 # This module is for replacing `dependent: :destroy` and `before_destroy` hooks.
 #

app/models/concerns/faster_cache_keys.rb

+# frozen_string_literal: true
+
 module FasterCacheKeys
   # A faster version of Rails' "cache_key" method.
   #

app/models/concerns/feature_gate.rb

+# frozen_string_literal: true
+
 module FeatureGate
   def flipper_id
     return nil if new_record?

app/models/concerns/ghost_user.rb

+# frozen_string_literal: true
+
 module GhostUser
   extend ActiveSupport::Concern

app/models/concerns/group_descendant.rb

+# frozen_string_literal: true
+
 module GroupDescendant
   # Returns the hierarchy of a project or group in the from of a hash upto a
   # given top.

app/models/concerns/has_status.rb

+# frozen_string_literal: true
+
 module HasStatus
   extend ActiveSupport::Concern

app/models/concerns/has_variable.rb

+# frozen_string_literal: true
+
 module HasVariable
   extend ActiveSupport::Concern

app/models/concerns/ignorable_column.rb

+# frozen_string_literal: true
+
 # Module that can be included into a model to make it easier to ignore database
 # columns.
 #

app/models/concerns/iid_routes.rb

+# frozen_string_literal: true
+
 module IidRoutes
   ##
   # This automagically enforces all related routes to use `iid` instead of `id`

app/models/concerns/importable.rb

+# frozen_string_literal: true
+
 module Importable
   extend ActiveSupport::Concern

app/models/concerns/issuable.rb

+# frozen_string_literal: true
+
 # == Issuable concern
 #
 # Contains common functionality shared between Issues and MergeRequests

app/models/concerns/loaded_in_group_list.rb

+# frozen_string_literal: true
+
 module LoadedInGroupList
   extend ActiveSupport::Concern

app/models/concerns/manual_inverse_association.rb

+# frozen_string_literal: true
+
 module ManualInverseAssociation
   extend ActiveSupport::Concern

app/models/concerns/mentionable.rb

+# frozen_string_literal: true
+
 # == Mentionable concern
 #
 # Contains functionality related to objects that can mention Users, Issues, MergeRequests, Commits or Snippets by

app/models/concerns/mentionable/reference_regexes.rb

+# frozen_string_literal: true
+
 module Mentionable
   module ReferenceRegexes
     def self.reference_pattern(link_patterns, issue_pattern)

app/models/concerns/milestoneish.rb

+# frozen_string_literal: true
+
 module Milestoneish
   def closed_items_count(user)
     memoize_per_user(user, :closed_items_count) do

app/models/concerns/note_on_diff.rb

+# frozen_string_literal: true
+
 # Contains functionality shared between `DiffNote` and `LegacyDiffNote`.
 module NoteOnDiff
   extend ActiveSupport::Concern

app/models/concerns/noteable.rb

+# frozen_string_literal: true
+
 module Noteable
   # Names of all implementers of `Noteable` that support resolvable notes.
   RESOLVABLE_TYPES = %w(MergeRequest).freeze

app/models/concerns/participable.rb

+# frozen_string_literal: true
+
 # == Participable concern
 #
 # Contains functionality related to objects that can have participants, such as