HEROKU_SLUG_COMMIT is deprecated and should use HEROKU_BUILD_COMMIT [JavaScript]

Initially raised in [https://github.com/getsentry/sentry-python/issues/5496](<https://github.com/getsentry/sentry-python/issues/5496>)