fix: allow install script in CI

[nbaztec]

Motivation

The current install script does not work in CI as source and export PATH are not supported by GHA. Additionally the script does not exit with failure in case of a failed verification.

Solution

• Detect $CI mode to directly add to both PATH and GITHUB_PATH instead.
• Exit with error code on verification failure.

[MexicanAce]

LGTM (minor nit, but not blocking)