test/: avoid integer overflow on 32 bit systems

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.