The taint mechanism will be deprecated in Ruby 2.7 (#1083)

The Ruby core team decided to deprecate the taint mechanism in Ruby 2.7
and will remove that in Ruby 3.

https://bugs.ruby-lang.org/issues/16131
ruby/ruby#2476

In Ruby 2.7, `Object#{taint,untaint,trust,untrust}` and related
functions in the C-API no longer have an effect (all objects are always
considered untainted), and are now warned deprecation message.

Author: kamipo

ext/mysql2/client.c

@@ -175,7 +175,7 @@ static void rb_mysql_client_mark(void * wrapper) {
 
 static VALUE rb_raise_mysql2_error(mysql_client_wrapper *wrapper) {
   VALUE rb_error_msg = rb_str_new2(mysql_error(wrapper->client));
-  VALUE rb_sql_state = rb_tainted_str_new2(mysql_sqlstate(wrapper->client));
+  VALUE rb_sql_state = rb_str_new2(mysql_sqlstate(wrapper->client));
   VALUE e;
 
   rb_enc_associate(rb_error_msg, rb_utf8_encoding());

ext/mysql2/statement.c

@@ -46,7 +46,7 @@ void rb_raise_mysql2_stmt_error(mysql_stmt_wrapper *stmt_wrapper) {
   VALUE e;
   GET_CLIENT(stmt_wrapper->client);
   VALUE rb_error_msg = rb_str_new2(mysql_stmt_error(stmt_wrapper->stmt));
-  VALUE rb_sql_state = rb_tainted_str_new2(mysql_stmt_sqlstate(stmt_wrapper->stmt));
+  VALUE rb_sql_state = rb_str_new2(mysql_stmt_sqlstate(stmt_wrapper->stmt));
 
   rb_encoding *conn_enc;
   conn_enc = rb_to_encoding(wrapper->encoding);