CLN: fix grammar in extract_index error message
The unit test result showed me I need to change the unit test also if it is grammar error. So, I will request it again.
 Yes, that is looking good! BTW, you don't have to open a new PR to update it, just push again and the PR will be updated automatically.
 Yes, sorry about it. Thanks for merging it. :)
 for future reference, this is merged in #8691
