Fix prettier-yaml restyler error. (#27277)

See
restyled-io/restyler#208 (comment) item
3: we are pinning a specific version of the prettier image, which means we have
to use a command syntax that works with that version.

.restyled.yaml

@@ -190,6 +190,9 @@ restylers:
     - name: prettier-yaml
       image: restyled/restyler-prettier:v1.19.1-2
       enabled: true
+      command:
+          - prettier
+          - "--write"
       include:
           - "**/*.yml"
           - "**/*.yaml"