Move remaining AUM tests to Fixed Function

On commit 2d75d3c0 several tests have been moved to Fixed Function in
order to follow the guideline to run all the AUM tests on this type of
images. However, apertis-update-manager-amd64-rollback test is still
run on HMI images, which has no sense. Move this test to Fixed
Function in order to follow the guideline.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>

test-cases/apertis-update-manager-amd64-rollback.yaml

@@ -2,7 +2,7 @@ metadata:
   name: apertis-update-manager-amd64-rollback
   format: "Apertis Test Definition 1.0"
   image-types:
-    hmi: [ amd64 ]
+    fixedfunction: [ amd64 ]
   image-deployment:
     - OSTree
   type: functional