Since the first minor version update has already been released, we can
probably feel comfortable updating to go1.21. This version now enforces
that the go version on the system is compatible with the version
specified in go.mod, so we can remove the old logic around checking the
minimum version in the Makefile.

- https://go.dev/doc/go1.21#tools

> To improve forwards compatibility, Go 1.21 now reads the go line in a go.work or go.mod file as a strict minimum requirement: go 1.21.0 means that the workspace or module cannot be used with Go 1.20 or with Go 1.21rc1. This allows projects that depend on fixes made in later versions of Go to ensure that they are not used with earlier versions. It also gives better error reporting for projects that make use of new Go features: when the problem is that a newer Go version is needed, that problem is reported clearly, instead of attempting to build the code and printing errors about unresolved imports or syntax errors.

Need to use the latest commit on the `go` branch, see:

- https://github.com/google/gvisor?tab=readme-ov-file#using-go-get

Is this why it is failing?