CompatHelper: bump compat for Adapt to 4, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Adapt package from 3.4 to 3.4, 4.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[nomadbl]

This passes all tests on my machine while using Adapt v4.0.0

julia> versioninfo()
Julia Version 1.11.0-DEV.1156
Commit ae9185b88c (2023-12-24 20:25 UTC)
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 2 × Intel(R) Xeon(R) CPU E5-2686 v4 @ 2.30GHz
  WORD_SIZE: 64
  LLVM: libLLVM-15.0.7 (ORCJIT, broadwell)
  Threads: 1 on 2 virtual cores```

[jeremiedb]

Is it possible to get the PR merged, this is needed for Flux: FluxML/Flux.jl#2362
@piever

[fhagemann]

+1

[christiangnrd]

Bump. Would be nice to have this merged and released soon so that packages that depend on this can also update compat.

[fhagemann]

Thanks!

[ViralBShah]

For folks who help maintain this package, I can also invite you to be contributors on the org. Please let me know who I should add.

[christiangnrd]

I'll take care of releasing v0.6.17 if you add me but I don't know how much I can contribute otherwise.

[christiangnrd]

Oh wait it seems like #291 (comment) is saying the next release might be 0.7. In that case I'd just backport the compat change in a new branch based off v0.6.16 and not risk breaking any current compatibility.