Simplify pipeline source policy pattern matching

lib/gitlab/ci/build/policy/refs.rb

@@ -27,7 +27,8 @@ module Gitlab
           def matches_pattern?(pattern, pipeline)
             return true if pipeline.tag? && pattern == 'tags'
             return true if pipeline.branch? && pattern == 'branches'
-            return true if source_to_pattern(pipeline.source) == pattern
+            return true if pipeline.source == pattern
+            return true if pipeline.source&.pluralize == pattern
 
             if pattern.first == "/" && pattern.last == "/"
               Regexp.new(pattern[1...-1]) =~ pipeline.ref
@@ -35,14 +36,6 @@ module Gitlab
               pattern == pipeline.ref
             end
           end
-
-          def source_to_pattern(source)
-            if %w[api external web].include?(source)
-              source
-            else
-              source&.pluralize
-            end
-          end
         end
       end
     end