fix: Install MySQL 8.4 on SLES 15 SP6

[algchoo]

Description

This PR updates MySQL installation test scripts to use version 8.4

Related issue

How has this been tested?

Checklist:

• Unit tests
  • Unit tests do not apply.
  • Unit tests have been added/modified and passed for this PR.
• Integration tests
  • Integration tests do not apply.
  • Integration tests have been added/modified and passed for this PR.
• Documentation
  • This PR introduces no user visible changes.
  • This PR introduces user visible changes and the corresponding documentation change has been made.
• Minor version bump
  • This PR introduces no new features.
  • This PR introduces new features, and there is a separate PR to bump the minor version since the last release already.
  • This PR bumps the version.

[schmikei]

In MySQL 8.4, this field is NULL (undefined or unknown) if the replication applier thread is not running, or if the applier thread has consumed all of the relay log and the replication receiver thread is not running. (In older versions of MySQL, this field was NULL if the replication applier thread or the replication receiver thread was not running or was not connected to the source.) If the replication receiver thread is running but the relay log is exhausted, Seconds_Behind_Source is set to 0.

I assume this may be the culprit for the failing SLES case. We may need to replicate and see what's going on in the integration test's returned value