use the superclass implementation
fix typo in Active Record Validations guide. [ci skip].

Closes #11498.
Upgrade guide. Renaming Indexes on tables. [ci skip].

https://github.com/rails/rails/commit/39eef1a565ef02e4dabc0811ef1bf4547ff9a60e#commitcomment-3672522
Merge pull request #11501 from nishantmodak/patch-3

Upgrade guide. Renaming Indexes on tables. [ci skip]
Fix test name typos
Merge pull request #11507 from vipulnsward/av_typo-4

Fix test name typos