[ruby/erb] Freeze ERB::Compiler::TrimScanner::ERB_STAG

(ruby/erb#100)

For Ractor compatibility.

ruby/erb@43f0876595

Author: osyoyu

lib/erb/compiler.rb

@@ -225,7 +225,7 @@ def explicit_trim_line(line)
       end
     end
 
-    ERB_STAG = %w(<%= <%# <%)
+    ERB_STAG = %w(<%= <%# <%).freeze
     def is_erb_stag?(s)
       ERB_STAG.member?(s)
     end