Update indexmap, bump MSRV

[westy92]

Updating indexmap to the latest version. Bump MSRV.

[AngelicosPhosphoros]

Hi! Thank you for pull request, I would merge it at the evening.

[AngelicosPhosphoros]

@westy92 The build failed for some reason. May you investigate?

[AngelicosPhosphoros]

Please, make Miri tests run using last available nightly with Miri component available.

[westy92]

I updated the nightly date to the day that 1.63 came out - that should fix things.

[AngelicosPhosphoros]

@westy92 Thank you for your contribution!

I would make a release today or tomorrow.

[westy92]

You're welcome!

[AngelicosPhosphoros]

I released 0.4.2

[westy92]

@AngelicosPhosphoros thank you so much! 🎉