Right shifting an high I256 does not work

[chikko80]

Version
ethers = 1.0.0 / 0.17.0 (same problem on old version)

Platform
M1 Mac, as well as x64 linux

Description
Bug? in bit-shifting an negative I256

[short summary of the bug]
When I try to right shift an I256 with 128 i get the wrong result - The result that is shows is 340282366920938463463374607431768090784 but the correct result is -120672

I tried this code:

use ethers::types::I256;

  fn main() {
      let negativ_number =
        I. 256::from_dec_str("-41062328663447644311028663865158126991809745").unwrap();
      dbg!(negativ_number >> 128);
  {

I expected to see this happen:

-120672

Instead, this happened: [explanation]

340282366920938463463374607431768090784

[mattsse]

cc @dbelv

[chikko80]

answered by @prestwich

use function asr()
the rightshift operator is implemented as a bitwise shift. asr() is the arithmetic right shift