[CI] set grenade to non-voting and drop grenade-skip-level

We introduced a change that breaks backwards compatibility with
older versions when listing services and providing filters [1].

When grenade branches were updated, manila tempest plugin started
failing and we need to set this job to non-voting to unblock the
gate.

Also, Hibiscus (2026.2) is not a SLURP release, we don't need
to run the skip-level-upgrade job.

[1] https://review.opendev.org/c/openstack/manila/+/928081

Change-Id: I93901d1125e5d85169bd5c4eb5d69fd46ba10f78
Signed-off-by: Carlos da Silva <ces.eduardo98@gmail.com>
Signed-off-by: Goutham Pacha Ravi <gouthampravi@gmail.com>

zuul.d/project.yaml

@@ -23,8 +23,8 @@
             voting: false
         - manila-tempest-plugin-lvm-fips-py311:
             voting: false
-        - manila-grenade
-        - manila-grenade-skip-level-always
+        - manila-grenade:
+            voting: false
         - manila-rally-no-ss:
             voting: false
         - manila-rally-ss: