Add additional note on reliable tests page

Why is this change being made?

This MR addresses the second checkbox of the following open issue #6678 (closed).

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what