Backport the Typescript 4.8+ fixes to io-ts 2.1.3

[psm14]

The fix to make io-ts compatible with Typescript 4.8 and newer was merged into the 2.2.x series of io-ts, but not the mutually incompatible 2.1.x series. I forked the repository and have a branch that applies the fix on top of 2.1.3 here: https://github.com/psm14/io-ts/tree/2.1.3-typescript-5-fix

Is it possible to get this upstreamed into a 2.1.4 release? I'd open a pull request, but there currently is no base branch to target. If so, let me know if there is anything I can do to help.