SOLR-16314: fix warnings about method visibility

[epugh]

https://issues.apache.org/jira/browse/SOLR-16314

Description

IntelliJ flagged we use private methods with our @Before etc annotations. They do actually get called however.

Solution

We have a mix of public and private, so lets just use public.

Tests

Ran tests

Checklist

Please review the following and check all that apply:

• [ ] I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• [ ] I have created a Jira issue and added the issue ID to my pull request title.
• [ ] I have given Solr maintainers access to contribute to my PR branch. (optional but recommended)
• [ ] I have developed this patch against the main branch.
• [ ] I have run ./gradlew check.
• [ ] I have added tests for my changes.
• [ ] I have added documentation for the Reference Guide