Error parsing the go.mod

[knechtionscoding]

When following install instructions:

hans.knecht:k6-runner/ (master✗) $ go install github.com/k6io/xk6/cmd/xk6@latest                                                                                                                                                                                                 

go: downloading github.com/k6io/xk6 v0.4.2
go: downloading github.com/Masterminds/semver/v3 v3.1.0

hans.knecht:k6-runner/ (master✗) $ xk6 build --with github.com/szkiba/xk6-prometheus@latest                                                                                                                                                                                      

2021/08/23 13:16:29 [INFO] Temporary folder: /Users/hans.knecht/Documents/Repositories/universe/infra/k6-runner/buildenv_2021-08-23-1316.046709920
2021/08/23 13:16:29 [INFO] Writing main module: /Users/hans.knecht/Documents/Repositories/universe/infra/k6-runner/buildenv_2021-08-23-1316.046709920/main.go
2021/08/23 13:16:29 [INFO] Initializing Go module
2021/08/23 13:16:29 [INFO] exec (timeout=10s): /usr/local/Cellar/go/1.16.5/libexec/bin/go mod init k6 
go: creating new go.mod: module k6
go: to add module requirements and sums:
        go mod tidy
2021/08/23 13:16:29 [INFO] Pinning versions
2021/08/23 13:16:29 [INFO] exec (timeout=0s): /usr/local/Cellar/go/1.16.5/libexec/bin/go mod edit -require go.k6.io/k6@latest 
2021/08/23 13:16:29 [INFO] exec (timeout=0s): /usr/local/Cellar/go/1.16.5/libexec/bin/go mod edit -require github.com/szkiba/xk6-prometheus@latest 
go: errors parsing go.mod:
/Users/hans.knecht/Documents/Repositories/universe/infra/k6-runner/buildenv_2021-08-23-1316.046709920/go.mod:5: require go.k6.io/k6: version "latest" invalid: must be of the form v1.2.3
2021/08/23 13:16:29 [INFO] Cleaning up temporary folder: /Users/hans.knecht/Documents/Repositories/universe/infra/k6-runner/buildenv_2021-08-23-1316.046709920
2021/08/23 13:16:29 [FATAL] exit status 1

This can be replicated with a minimalist dockerfile:

# Build the k6 binary with the extension
FROM golang:1.16.4-buster as builder

RUN go install github.com/k6io/xk6/cmd/xk6@latest
RUN xk6 build --output /k6 --with github.com/szkiba/xk6-prometheus@latest

I've also tried increasing the golang version to 1.16.7 (latest stable in that minor version). without and change.