Update pragma to 0.8.20 (#4489)

Co-authored-by: Francisco Giordano <fg@frang.io>
Co-authored-by: ernestognw <ernestognw@gmail.com>

contracts/utils/Strings.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // OpenZeppelin Contracts (last updated v4.9.0) (utils/Strings.sol)
 
-pragma solidity ^0.8.19;
+pragma solidity ^0.8.20;
 
 import {Math} from "./math/Math.sol";
 import {SignedMath} from "./math/SignedMath.sol";