Fix agent mutation of new registry (#845)

## Description

This is a hotfix related to the image SHASUMs introduced recently to not
mutate the zarf registry on a zarf reinit.

## Related Issue

Fixes # N/A

## Type of change

- [X] Bug fix (non-breaking change which fixes an issue)

## Checklist before merging

- [X] (Optional) Changes have been linted locally with
[golangci-lint](https://github.com/golangci/golangci-lint). (NOTE: We
haven't turned on lint checks in the pipeline yet so linting may be hard
if it shows a lot of lint errors in places that weren't touched by
changes. Thus, linting is optional right now.)

Co-authored-by: Megamind <[email protected]>

packages/zarf-registry/registry-values.yaml

@@ -27,3 +27,6 @@ resources:
     memory: "2Gi"
 
 fullnameOverride: "zarf-docker-registry"
+
+podLabels:
+  zarf.dev/agent: "ignore"