Versions prior to 1.5.4 don't have checksum files available, which renders them impossible to install

[vyneer]

Describe the bug
It seems like a .sha256 file only started getting provided with the downloads somewhere in 2016, which leads to this plugin being unable to install versions older than that because of a failed checksum check.

To Reproduce
Steps to reproduce the behavior:

1. asdf install golang 1.5.3
2. See error

Expected behavior
Go version 1.5.3 installs.

Screenshots

Desktop

• OS: Arch Linux 6.0.7.zen1-1 amd64
  and
• OS: Windows WSL 5.15.68.1-microsoft-standard-WSL2

Additional context
It seems like the Go team is aware of the issue, and they're planning on adding the missing checksums eventually (golang/go#45608). They are also missing from the go.dev/dl JSON list, but there are SHA1 checksums available on the plain https://go.dev/dl page.

Not sure what's the best way to go about fixing this, but, if possible to implement, maybe some kind of --skip-checksum flag or SKIP_CHECKSUM=1 env var to bypass the check would be helpful.

[kennyp]

I think something like an ASDF_GOLANG_SKIP_CHECKSUM env var makes sense. I'll work on putting together a PR.