🐛(frontend) fix Enroll now translation

[igobranco]

When using an external LMS, the CTA Enroll now on course runs isn't being translated.

Screenshot on french, is still showing the Enroll now on english.

After applying this fix and translate it on src/frontend/i18n/locales/fr-FR.json:

"components.SyllabusCourseRun.enroll": {
    "description": "CTA for users who can enroll in the course run or could enroll if they logged in.",
    "message": "S’inscrire maintenant"
  },