golang: include go.env in GOROOT

[mfrw]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./SPECS/LICENSES-AND-NOTICES/data/licenses.json, ./SPECS/LICENSES-AND-NOTICES/LICENSES-MAP.md, ./SPECS/LICENSES-AND-NOTICES/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

---

Summary

What does the PR accomplish, why was it needed?
Include go.env in GOROOT which is now the default value from where GOPROXY value is read

Cherry-Pick of: #8004

Change Log

• Include go.env in GOROOT

Does this affect the toolchain?

NO

Associated issues

• cmd/go: go mod download breaks on 1.21.0 due to empty GOPROXY  golang/go#61928

Links to CVEs

• NA

Test Methodology

• Pipeline build id: PR-8021

/cc @dagood

[kanikanema]

LGTM

[dagood]

This also sets GOTOOLCHAIN=local, which is important for Mariner to avoid accidentally downloading "official" Go builds in CI: https://github.com/microsoft/go/blob/v1.21.6-1/patches/0008-Update-default-go.env.patch

/cc @qmuntal @gdams