Fixed custom validation context bug where child
associations were not being saved.

Fixes #13854.

[Eric Chahin, Aaron Nelson, & Kevin Casey]
[ci skip] Update guides license to CC BY-SA 4.0 International.

Benefits: https://creativecommons.org/version4
Added link for 4.1 guides on edge guide [ci skip]
Tiny follow up to #14915 [ci skip]
Automaticly add username and email if configured in git-scm, as bundle gem
Works correctly if git not installed
skip-git should not hit git commands plugin generators
Merge pull request #14941 from arunagw/hbakhtiyor-new-plugin-command-advanced-config

Plugin gemspec
Merge pull request #14942 from JuanitoFatas/patch/cc-by-sa-4-0

[ci skip] Update guides license to CC BY-SA 4.0 International.
Add singular and plural form for some validation messages
Merge pull request #14943 from arunagw/hbakhtiyor-i18n-validation-message-singular-and-plural

Add singular and plural form for some validation messages
eliminate repetition in guide links for past releases [ci skip]
passing a nil should always raise an ArgumentError
push up bind params on "simple" subquery calculations

bind parameters we not being propogated to simple subquery calculation
calls. This fixes it
make `db:structure:load` listed with `rake -T`
passing a nil in the polymorphic array is not supported. remove nils before you call the method
Move dup destroyed test to specific file that tests dup logic

Also change other related test to use existing record rather than
creating new one.
Add branch to arel on Gemfile to allow local bundle config [ci skip]
Add missing require to fix test :bomb:
Use #include? instead of #any?, make it simpler