test: Fix build with !HAVE_LZ4 && HAVE_XZ

test: Fix build with !HAVE_LZ4 && HAVE_XZ

HUGE_SIZE was defined inconsistently.

> In file included from ../src/basic/alloc-util.h:9,
>                  from ../src/journal/test-compress.c:9:
> ../src/journal/test-compress.c: In function ‘main’:
> ../src/journal/test-compress.c:280:33: error: ‘HUGE_SIZE’ undeclared (first use in this function)
>   280 |         assert_se(huge = malloc(HUGE_SIZE));