Suppress SyntaxError during RubyVM::AST.of

When the original source code is erb, RubyVM::AST.of does not work well.
rails/rails#42678.

Author: mame

lib/error_highlight/core_ext.rb

@@ -29,7 +29,7 @@ def to_s
 
         spot = ErrorHighlight.spot(node, **opts)
 
-      rescue Errno::ENOENT
+      rescue Errno::ENOENT, SyntaxError
       end
 
       if spot