Add new corretto21 distribution of OpenJDK 21 LTS

[GoKuroko]

Verification

• I understand that if I ignore these instructions, my issue may be closed without review.
• I have retried my command with --force.
• I ran brew update-reset && brew update and retried my command.
• I ran brew doctor, fixed as many issues as possible and retried my command.
• I have checked the instructions for reporting bugs.
• I made doubly sure this is not a checksum does not match error.

Description of issue

As all we known, JDK21 has become the next long-term support version. So, people may expect to stay in the LTS version instead of an unpredictable cask that keeps scrolling every half-year.

Hope you can approve the corretto21's pull request. #17823

Command that failed

brew install --cask corretto21

Output of command with --verbose --debug

Not relevant.

Output of brew doctor and brew config

Not relevant.

Output of brew tap

Not relevant.

[miccal]

Version 21 of Amazon Corretto is available in the main homebrew-cask repository. Once version 22 is released, the version in the main repository will be updated to version 22 and only then we can add version 21 to the homebrew-cask-versions repository.

[GoKuroko]

However, the Zulu21 has been merged to the homebrew-cask-version repository. I think this doesn't conform to the rules you described. #17757 @miccal

https://github.com/Homebrew/homebrew-cask-versions/blob/master/Casks/zulu21.rb
https://github.com/Homebrew/homebrew-cask/blob/master/Casks/z/zulu.rb

[miccal]

Adding zulu21 was an error -- Casks in the homebrew-cask-versions repository should not in general match those in the main homebrew-cask repository.