As TimVP pointed out, a previous change enabled some previously-skipped
texture gather 2d_array tests. Enabling them.

Bug: angleproject:3605
Bug: angleproject:3189
Change-Id: I3ad190131339a04441fdd05e23ff3b7ac724dc83
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1797655Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Tobin Ehlis <tobine@google.com>