Fix error string commas.
Fix error string commas.

For example: 1, 2, 3, 4 became 1 = 2 = 3 = 4.

These were acidentally changed to equals signs way back in this CL:

610640fabee9 "Don't use gl::Error in validation."

Bug: angleproject:4067
Change-Id: I05d1c5ecc5f6fb7636f81ca59d05928dd940bf8d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1890631
Reviewed-by: Yuly Novikov <36f5580f63d0a3eacc17e89a61d11e2f646630d2@chromium.org>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle