goinstallscript: Add tests for `-AzurePipelinePath` and `-GitHubActionsPath`

[dagood]

-AzurePipelinePath and -GitHubActionsPath cause go-install.ps1 to set up PATH in CI pipelines written in Azure Pipelines and GitHub Actions respectively. We don't currently have any tests that the logging command is sent as expected or that $GITHUB_PATH is written to.