Reuse the possible characters so that we never miss

Feedback:
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2112#note_32338043

lib/ee/gitlab/regex.rb

 module EE
   module Gitlab
     module Regex
+      def variable_scope_regex_chars
+        "#{environment_name_regex_chars}\\*"
+      end
+
       def variable_scope_regex
-        @variable_scope_regex ||= /\A[a-zA-Z0-9_\\\/\${}. -*]+\z/.freeze
+        @variable_scope_regex ||= /\A[#{variable_scope_regex_chars}]+\z/.freeze
       end
 
       def variable_scope_regex_message

lib/gitlab/regex.rb

@@ -39,8 +39,12 @@ module Gitlab
       @container_repository_regex ||= %r{\A[a-z0-9]+(?:[-._/][a-z0-9]+)*\Z}
     end
 
+    def environment_name_regex_chars
+      'a-zA-Z0-9_/\\$\\{\\}\\. -'
+    end
+
     def environment_name_regex
-      @environment_name_regex ||= /\A[a-zA-Z0-9_\\\/\${}. -]+\z/.freeze
+      @environment_name_regex ||= /\A[#{environment_name_regex_chars}]+\z/.freeze
     end
 
     def environment_name_regex_message