gitlab: make the schedule rules a bit more general

By default no jobs should run under the schedule and then we can be
more explicit for the ones that we need to. Otherwise I trigger all my
custom runners every time I do a scheduled run.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20251117115523.3993105-18-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

.gitlab-ci.d/base.yml

@@ -45,8 +45,8 @@ variables:
     - if: '$CI_PROJECT_NAMESPACE == $QEMU_CI_UPSTREAM && $CI_COMMIT_TAG'
       when: never
 
-    # Scheduled runs on mainline don't get pipelines except for the special Coverity job
-    - if: '$CI_PROJECT_NAMESPACE == $QEMU_CI_UPSTREAM && $CI_PIPELINE_SOURCE == "schedule"'
+    # Scheduled jobs should explicitly enable the run in their job rules
+    - if: '$CI_PIPELINE_SOURCE == "schedule"'
       when: never
 
     # Cirrus jobs can't run unless the creds / target repo are set