Since the RAII-based GLRenderbuffer goes away at the end of the test
function, we should end the render pass before ending the test.

Bug: chromium:1122621
Change-Id: I5aaf2a0b4fd63a38fc5018830ee4e9d7d93f0c81
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2380248Reviewed-by: Cody Northrop <cnorthrop@google.com>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Commit-Queue: Ian Elliott <ianelliott@google.com>