CI: pin the benchmark job to ubuntu-jammy

The default is 24.04 "Noble" which does not work with Bifrost yet.

Change-Id: I6bb99402190712852bdfe7f83df32c12390cca85

Author: dtantsur

zuul.d/bifrost-jobs.yaml

@@ -223,6 +223,7 @@
 - job:
     name: bifrost-benchmark-ironic
     parent: bifrost-base
+    nodeset: ubuntu-jammy
     timeout: 7200
     run: playbooks/ci/benchmark-ironic.yaml