CI: restore Go integ tests

## Problem

#3551 switched the integ tests CodeBuild CI spec to run tests as unprivileged (non-root) user, in part to fix #3550 .

But the `goenv` and `go` commands fail now, and had to be disabled:

# Install latest version of Go (known to 'goenv')
# - eval "$(goenv init -)"
# - 'export PATH="$GOROOT/bin:$PATH:$GOPATH/bin"'
# - '>/dev/null VERSION=$(goenv install --list | tail -n 1) && 2>/dev/null goenv install $VERSION'
# - '>/dev/null goenv global $VERSION && go env -w GOPROXY=direct'
# - go version

## Expectation

Restore use of `go` in the integ tests and re-enable the tests disabled in https://github.com/aws/aws-toolkit-vscode/pull/3551/commits/fab07b3fe1047353896737fa64bcca910d3d28a9

Start by reviewing the CodeBuild CI specification changes from #3551 and commit fab07b3fe1047353896737fa64bcca910d3d28a9, focusing on the disabled goenv and Go commands. Run the integration-test workflow to reproduce the unprivileged-user failures. Done means Go is available in the workflow and the disabled integration tests run successfully again.

Written by the indexing model from the issue text.