make Rails 7.0 applicable

[kanipan]

This updates the gem usable with Rails 7.0 or above.

[kanipan]

Since the five major repositories have been updated to 2.4.21, we will align this one as well.
5 大リポジトリが 2.4.21 になっていたのでこちらも合わせる

[kanipan]

Since Rails 7 requires Ruby 2.7 or higher, I updated to the latest version of 2.7.
Rails 7 は Ruby 2.7 以上が必要なので 2.7 の最新にした

[kanipan]

same as https://github.com/Fablic/multi-cache-rails/pull/5/files#r1663425972

[kanipan]

I removed the unused Rails versions.

[kanipan]

In the past, various versioning methods were used without any apparent rules, so to keep things simple, I opted for a patch version update
過去に色々なバージョンの切り方をされておりルールがなさそうだったので面倒だからパッチバージョンアップにしておいた

[kanipan]

と思ったけど engine 側で ~> 5.2.0 となっており、Rails 7 アップデートと共にこの gem も上げたいのでマイナーバージョンを上げる事にした

[nagamine-r]

LGTM!

[icer7]

LGTM!

[icer7]

LGTM!

[nagamine-r]

LGTM again

[kanipan]

The git tags were created manually.
タグは手動で作った

$ git checkout master
$ git pull --rebase origin master
$ git tag v5.3.0
$ git push origin v5.3.0

The release notes were manually created as well, based on the existing ones
リリースノートも既存のものを参考に手動で作った

https://github.com/Fablic/multi-cache-rails/releases/tag/v5.3.0