generic/574: test corruption at more offsets

generic/574: test corruption at more offsets

Expand generic/574 to test for corruption in more different parts of the
file to try to exercise any hashing optimizations that might be used.

There is no existing bug that this finds.  This is just to prevent
future bugs, considering optimizations along the lines of
https://lore.kernel.org/fsverity/20240611034822.36603-7-ebiggers@kernel.org/

Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Andrey Albershteyn <aalbersh@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>