fix: unicorn flavor proxy image reference (#590)

## Description

Makes the same change as
#513 for the `unicorn`
flavor.
## Related Issue

Related to #513

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [x] Test, docs, adr added or updated as needed
- [x] [Contributor
Guide](https://github.com/defenseunicorns/uds-template-capability/blob/main/CONTRIBUTING.md)
followed

src/istio/values/unicorn-values.yaml

@@ -1,7 +1,9 @@
 pilot:
-  image: cgr.dev/du-uds-defenseunicorns/istio-pilot-fips:1.22.2
+  image: "cgr.dev/du-uds-defenseunicorns/istio-pilot-fips:1.22.2"
 global:
   proxy_init:
-    image: cgr.dev/du-uds-defenseunicorns/istio-proxy-fips:1.22.2
+    # renovate: image=cgr.dev/du-uds-defenseunicorns/istio-proxy-fips
+    image: "###ZARF_REGISTRY###/du-uds-defenseunicorns/istio-proxy-fips:1.22.2"
   proxy:
-    image: cgr.dev/du-uds-defenseunicorns/istio-proxy-fips:1.22.2
+    # renovate: image=cgr.dev/du-uds-defenseunicorns/istio-proxy-fips
+    image: "###ZARF_REGISTRY###/du-uds-defenseunicorns/istio-proxy-fips:1.22.2"