Change flags type in Http2FrameHeaderTypeAndFlagTest.
Change flags type in Http2FrameHeaderTypeAndFlagTest.

External contribution by tmoniuszko-opera at
https://github.com/google/quiche/pull/14.

Listing tests with --gtest_list_tests prints non-UTF-8 characters.
This change is to fix that.  See pull request for more details and
for why this matters.

PiperOrigin-RevId: 446459944

google/quiche,google/quiche,google/quiche,google/quiche