Initialize FrameInfo rotation in GenericDecoderTest

GenericDecoderTest color-space cases construct FrameInfo directly. The default constructor leaves rotation uninitialized, which can trip UBSan when GenericDecoder reads the enum.

Initialize rotation to kVideoRotation_0 in both tests.

Bug: webrtc:514423244
Change-Id: Ifebf07c0e4d0489ff87cb58d65ec6a7d7e7fd00e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/473520
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Boris Tsirkin <btsirkin@meta.com>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47734}