Simplify pull_request Konflux build

The multiarch build isn't a requirement for pull
requests.

Signed-off-by: Dale Haiducek <[email protected]>

Author: dhaiducek

.tekton/cluster-api-provider-kubevirt-mce-29-pull-request.yaml

@@ -29,9 +29,6 @@ spec:
   - name: build-platforms
     value:
     - linux/x86_64
-    - linux/ppc64le
-    - linux/s390x
-    - linux/arm64
   - name: dockerfile
     value: Dockerfile.rhtap
   - name: path-context