.cirrus.yml: fix a warning

Cirrus CI emits a bunch of warnings like this one:

> task "success" depends on task "fedora-38 vfs", but their only_if conditions are different

This was probably copied from another repo, which uses CI:DOCS magic to
skip some tests. In this repo, it is not used, so remove the condition.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.cirrus.yml

@@ -56,7 +56,6 @@ gce_instance:
 linux_testing: &linux_testing
     depends_on:
         - lint
-    only_if: $CIRRUS_CHANGE_TITLE !=~ '.*CI:DOCS.*'
     gce_instance:  # Only need to specify differences from defaults (above)
         image_name: "${VM_IMAGE}"