Update outdated test certificates

What does this MR do?

This updates the outdated test certificates because they expired May 13 07:54:55 2025 GMT.

Updated as per test/testdata/mutualtls/valid/README.md.

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines