Potential issue migrating from v2beta29 -> v3alpha1 when using `custom` builder

[aaron-prindle]

Noticed the following possible error when updating our examples/:

Seems the image: replacement might not work when used with ko:// or other alternate image formats? This is the output from skaffold fix I assume, I manually added this back in examples/ but this could bite other users when migrating custom builders from v2beta29 -> v3alpha1