CoreCI's buildIsolatedEnv does NOT forward GOROOT, GOPATH, GOCACHE,
GOMODCACHE (they're in the systemVars deny-list in pass_through.go).
The shell-isolated executor's env only has PATH, HOME, LANG, TMPDIR,
TERM, CI + CORECI_* + CI_* + job vars. Without GOMODCACHE/GOCACHE, Go
commands fail (can't find module/build cache). Fix: re-derive them from
the go binary on PATH via 'go env GOROOT' etc.
---ci---
project: orca
phase: 1
milestone: v0.16
status: execute
---/ci---
Jon Chery
4a97cb1ea2