Add missing LEX_STRING::strs for my_snprintf

When these members switched from plain `char*` to `LEX_CSTRING`,
not all usages were converted. Specifically, in this commit are args of
`my_snprintf` derivatives. Because until MDEV-21978,
automated type checks were unavailable for those functions due to
their incompatibility, so these tools didn’t catch them.

Author: ParadoxV5

sql/mysqld.cc

@@ -5732,7 +5732,7 @@ static void test_lc_time_sz()
         (*loc)->max_day_name_length != max_day_len)
     {
       DBUG_PRINT("Wrong max day name(or month name) length for locale:",
-                 ("%s", (*loc)->name));
+                 ("%s", (*loc)->name.str));
       DBUG_ASSERT(0);
     }
   }

sql/sys_vars.cc

@@ -6063,7 +6063,7 @@ static bool check_locale(sys_var *self, THD *thd, set_var *var)
     {
       push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
                           "Can't process error message file for locale '%s'",
-                          locale->name);
+                          locale->name.str);
       return true;
     }
   }

storage/maria/ha_maria.cc

@@ -2079,7 +2079,7 @@ int ha_maria::enable_indexes(key_map map, bool persist)
     {
       sql_print_warning("Warning: Enabling keys got errno %d on %s, "
                         "retrying",
-                        my_errno, file->s->open_file_name);
+                        my_errno, file->s->open_file_name.str);
       /* Repairing by sort failed. Now try standard repair method. */
       param->testflag &= ~T_REP_BY_SORT;
       file->state->records= start_rows;