SOLR-17406: Update labeler.yml to correctly set dependency label

[malliaridis]

https://issues.apache.org/jira/browse/SOLR-17406

Description

With the updates from #2706 the GitHub action does not take the new gradle/libs.version.toml into account when setting the dependencies label.

Solution

Add gradle/libs.versions.toml to the watched file list of the dependencies label.

Note that we still want to keep versions.props in the list to also label 9X PRs that make changes in the versions.props file.

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, not available for branches on forks living under an organisation)
• 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