Fix argument names in http2_structures_test_util.cc.
Fix argument names in http2_structures_test_util.cc.

ClangTidy is complaining that argument names do not match between declarations
and definitions.

PiperOrigin-RevId: 347911111
Change-Id: Ib132f2ac4ec94eb1d11776d28dcc0d72ac939237

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