Fix schedule rules ordering

Why is this change being made?

!2568 (merged) was supposed to fix gitlab-org/gitlab#337366 (closed), but I made a blunder regarding the rules ordering.

According to the docs:

Rules are evaluated in order until the first match. When a match is found, the job is either included or excluded from the pipeline, depending on the configuration.

Since the positive conditions are met before $CI_PIPELINE_SOURCE == "schedule", the job is included despite the attempt to exclude scheduled jobs. Negative assertions need to go before any positive assertions to ensure that they are excluded.