Update pragma to 0.8.20 (#4489)

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

scripts/generate/templates/EnumerableMap.js

@@ -10,7 +10,7 @@ const TYPES = [
 
 /* eslint-disable max-len */
 const header = `\
-pragma solidity ^0.8.19;
+pragma solidity ^0.8.20;
 
 import {EnumerableSet} from "./EnumerableSet.sol";