Fix: parse identifier with backquote

lib/active_record/turntable/sql_tree_patch.rb

@@ -52,6 +52,7 @@ def each_token(&block) # :yields: SQLTree::Token
       when /\w/;           tokenize_keyword(&block)
       when OPERATOR_CHARS; tokenize_operator(&block)
       when SQLTree.identifier_quote_char; tokenize_quoted_identifier(&block)
+      when SQLTree.identifier_quote_field_char; tokenize_identifier_with_quote(&block)
       end
     end
 
@@ -73,6 +74,14 @@ def tokenize_possible_escaped_string(&block)
       tokenize_keyword(&block)
     end
   end
+
+  def tokenize_identifier_with_quote(&block)
+    next_char # skip identifier_quote_field_char
+    literal = current_char
+    literal << next_char while SQLTree.identifier_quote_field_char != peek_char
+    next_char # skip identifier_quote_field_char
+    handle_token(SQLTree::Token::Identifier.new(literal), &block)
+  end
 end
 
 module SQLTree::Node