Fix examples of number_to_percentage

[ci skip]
Use the canonical router on the CHANGELOG entry

Thanks @egilburg

[ci skip]
Revert "Fix SyntaxError in guides sample code"

This reverts commit f573df32d43c413a5098721ba6151ff190c23c6c.

The original idea of this documentation was to showcase the feature
where you can remove some only queries attributes with a single
key-value pair.
remove duplication in test
Merge pull request #11491 from erichkist/ek-revert-unscope-patch

Revert "Fix SyntaxError in guides sample code"
Merge pull request #11492 from maratvmk/concern_test

remove duplication in concern_test
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
Extract verbs array from helper to a constant
Merge pull request #11508 from vipulnsward/extract_constants

Extract verbs array from helper to a contant
Removed information about creating database[ci skip]

- As default index page is no longer in public folder, rails hits the
  welcome controller in railties for index action
- If the database is not created or username and password are
  incorrect in database.yml, those errors are first shown before index
  action succeeds
- welcome#index succeeds iff the database is created with correct
  details in database.yml
- So this information about creating database is not required in the
  index template