Do not inherit credentials when setting a registry URL

### Jenkins and plugins versions report

-

### What Operating System are you using (both controller, and any agents involved in the problem)?

Linux

### Reproduction steps

1. Set a registry with credentials globally.
2. Specify a `registryUrl` in a `docker {}` block without credentials

### Expected Results

Do not use the globally configured registry credentials.

### Actual Results

Inherits the globally configured value.

### Anything else?

I suppose, it could make sense to also have a way to simply disable the use of a globally configured registry in case one wants to use an image that already exists locally.

### Are you interested in contributing a fix?

_No response_