test/: avoid integer overflow on 32 bit systems

[mschauer]

After the fix of #5142 I am running the tests in 32 bit. These are
three smaller fixes to the tests for 32 bit systems fixing tests assuming 64bit ints.

while loading euler.jl, in expression starting on line 70
ERROR: test failed: :((sum(primes(2000000))==142913828922))

while loading ranges.jl, in expression starting on line 105
ERROR: test failed: :((length(1:4:typemax(Int64))==2305843009213693952))

while loading mod2pi.jl, in expression starting on line 193
ERROR: test failed: :((mod2pi(^(2,60))==mod2pi(^(2.0,60))))

One might argue that length(1:4:typemax(Int64)) should actually throw an error as Range.len is of type Int32 there.

[staticfloat]

Thanks for this, @mschauer!