[TEST] fix off-by-one error in BigArrays tests

Comparisons for the BigArrays breaker use "greater than" instead of
"greater than or equal", which was never an issue before because the
test size was not right on a page boundary. A test with an exactly
divisible page boundary (4mb exactly in this case) caused the sizes to
be equal to, but not exceed, the limit, and never break.

The limit should be smaller than the test increments the breaker anyway.