Add Changelog entry for job-level variables

CHANGELOG

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.7.0 (unreleased)
   - Method instrumentation now uses Module#prepend instead of aliasing methods
   - Repository.clean_old_archives is now instrumented
+  - Add support for environment variables on a job level in CI configuration file
   - The Projects::HousekeepingService class has extra instrumentation
   - All service classes (those residing in app/services) are now instrumented
   - Developers can now add custom tags to transactions