- Fixed unused variable
- Changed test to verify complete message instead of verifying if message contains text.
Add 'require' for Hash#with_indifferent_access

ActiveJob::Arguments uses Hash#with_indifferent_access.
But, activejob gem does not require Hash extension library.
When we use activejob as standalone,
we need extra require statement. This is unhandy.

This commit fixes it.
Testing guide grammar fix

[skip ci]
Merge pull request #18124 from jonatack/patch-8

Testing guide grammar fix
Merge pull request #18119 from joker1007/add_require_core_ext_hash_to_activejob

Add 'require' for Hash#with_indifferent_access to active_job/arguments.rb
Merge pull request #18118 from vipulnsward/fix-validation-message

Validation test fixes
Remove bullet
Merge pull request #18126 from Decagon/patch-1

Remove extra bullet in README.md [ci skip]