Support React v18

[koba04]

React v18 is now in beta, so it's time to prepare for the release.
This is the meta issue for what we need.

• 🏃‍♂️ Test with React 18 test: Add React 18 to test matrix #771

[koba04]

React v18 RC has been released.

[koba04]

I believe react-transition-group works well with React v18, so I'll close this 🎉

[tranvansang]

#775 (comment)

I believe react-transition-group works well with React v18, so I'll close this tada

Unfortunately, it is not :'(. I have made another issue on react 18.

#816