Enable frozen string in vestigial files

Partially addresses #47424.

app/models/concerns/project_services_loggable.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ProjectServicesLoggable
   def log_info(message, params = {})
     message = build_message(message, params)

app/models/hooks/active_hook_filter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ActiveHookFilter
   def initialize(hook)
     @hook = hook

app/validators/branch_filter_validator.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # BranchFilterValidator
 #
 # Custom validator for branch names. Squishes whitespace and ignores empty

app/validators/js_regex_validator.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class JsRegexValidator < ActiveModel::EachValidator
   def validate_each(record, attribute, value)
     return true if value.blank?

changelogs/unreleased/frozen-string-enable-vestigial.yml

@@ -0,0 +1,5 @@
+---
+title: Enable frozen string in vestigial files
+merge_request:
+author: gfyoung
+type: performance