Fix ExternalBufferTest end2end test The application or test should be responsible for managing the lifetime of external buffer ensuring that the external buffer is not deleted as long as there are any GL buffer objects referring to it. https://registry.khronos.org/OpenGL/extensions/EXT/EXT_external_buffer.txt Bug: b/396231708 Change-Id: Ib8e7e2ef0349cadc42b839019e2b2334b4cc5085 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6502674 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com>