neutron: use YAML literal for ironic_ml2_baremetal patch

The | block is required so the value is a string passed to
oc patch --patch. A nested mapping serializes to invalid JSON
and the API rejects the merge patch.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: ciecierski

tests/roles/neutron_adoption/defaults/main.yaml

@@ -31,7 +31,7 @@ neutron_config_patch: |
         - internalapi
 neutron_retry_delay: 5
 
-ironic_ml2_baremetal_patch:
+ironic_ml2_baremetal_patch: |
   spec:
     neutron:
       template: