Make FsVerityTest explicitly use an uncompressed file

Fix a test failure on devices that have 'compress_extension=*' in their
fstab by explicitly setting the test file to uncompressed.

Bug: 440971743
Test: atest FsVerityTest # Cuttlefish with current fstab
Test: atest FsVerityTest # Cuttlefish with 'compress_extension=*' added to fstab
Test: atest FsVerityTest # Cuttlefish with 'fscompress' removed from fstab
Flag: EXEMPT TEST_ONLY
Change-Id: Ib8ce595be1dd75269a09c78ea866ac391f4f2d89