Sqrt does not work properly for fields F_p where p = 5 mod 8

[juja256]

Sqrt computation hangs forever for custom fields where p = 5 mod 8 in the current version of ark_ff

Minimum reproducible example:

use ark_ff::{fields::{Fp256, MontBackend, MontConfig}, BigInteger, Field, PrimeField};

// custom field with p = 5 mod 8
#[derive(MontConfig)]
#[modulus = "7237005577332262213973186563042994240857116359379907606001950938285454250989"]
#[generator = "5"]
pub struct FqConfig;
pub type Fq = Fp256<MontBackend<FqConfig, 4>>;

// this code just runs infinitely
#[test]
fn test_sqrt() {
    for i in 0..10000 {
        let a = Fq::from(i);
        let b = a * a;
        let c = b.sqrt().unwrap();
        assert!(c == a || c == -a);
    }
}

We have already proposed a solution in PR for this fields.