Credential validity check does not work for credentials-admin

### Jenkins and plugins versions report

n/a

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

n/a

### Reproduction steps

https://github.com/jenkinsci/aws-credentials-plugin/blob/5aec8d32b4c7f32cd3a4e39946290eed53e4edf7/src/main/java/com/cloudbees/jenkins/plugins/awscredentials/AWSCredentialsImpl.java#L370-L373

I have the credentials-admin role on our CloudBees controller. However, because of this overly restrictive check, I can no longer rely on this plugin to verify that the AWS credentials I am configuring are correct before saving them. This makes credential rotation risky.

### Expected Results

Anyone who can set the credentials ought to be able to test their validity.

### Actual Results

The check no longer happens for credentials-admin.

### Anything else?

_No response_

### Are you interested in contributing a fix?

_No response_

Start at src/main/java/com/cloudbees/jenkins/plugins/awscredentials/AWSCredentialsImpl.java around lines 370-373 and inspect the credential validity check and its permission condition. Trace the related tests or plugin test suite to understand the existing behavior. Done means credentials-admin users can test configured AWS credentials before saving, without weakening access controls.

Written by the indexing model from the issue text.