Update pragma to 0.8.20 (#4489)

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

docs/modules/ROOT/pages/erc20.adoc

@@ -15,7 +15,7 @@ Here's what our GLD token might look like.
 ----
 // contracts/GLDToken.sol
 // SPDX-License-Identifier: MIT
-pragma solidity ^0.8.19;
+pragma solidity ^0.8.20;
 
 import {ERC20} from "@openzeppelin/contracts/token/ERC20/ERC20.sol";