How to add Build time env var through doctl in a Functions namespace

I’ve recently started working with “Functions” service in Golang. As I understand, I need a namespace to test it out with doctl, and it seems to me that it is totally different than App Platform.

Now a need to use a private Go module from GitHub has arised, and I found out from this and this documentation that I need to set a GO_GIT_CRED__HTTPS__GITHUB__COM build time env var. I know I can do it in App Platform, but I need to do the same in a namespace, so that I can test it out locally using doctl and push it to the Production App Platform.

So far I have tried to add the above env var into project.yml but it seems unfruitful. I get the following:

go mod download: github.com/CyberCitizen01/HighLow/core@v0.0.0-20221219074058-5e7784f2218b: invalid version: git fetch -f origin refs/heads/*:refs/heads/* refs/tags/*:refs/tags/* in /tmp/go/pkg/mod/cache/vcs/642ca7a2cf3bf96e7ac2e10395c4ae76f4d7bb66b0d13784004f523d66c63b37: exit status 128:
        fatal: could not read Username for 'https://github.com': terminal prompts disabled

Note: I’ve tried the username:pat syntax for GO_GIT_CRED__HTTPS__GITHUB__COM and yet it results in the same above error.