Fix guides for 5.0 (#4654)

Co-authored-by: Ernesto García <ernestognw@gmail.com>
(cherry picked from commit e12511b53e)

contracts/mocks/docs/ERC20WithAutoMinerReward.sol

@@ -0,0 +1,22 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {ERC20} from "../../token/ERC20/ERC20.sol";
+
+contract ERC20WithAutoMinerReward is ERC20 {
+    constructor() ERC20("Reward", "RWD") {
+        _mintMinerReward();
+    }
+
+    function _mintMinerReward() internal {
+        _mint(block.coinbase, 1000);
+    }
+
+    function _update(address from, address to, uint256 value) internal virtual override {
+        if (!(from == address(0) && to == block.coinbase)) {
+            _mintMinerReward();
+        }
+        super._update(from, to, value);
+    }
+}

contracts/mocks/docs/MyContractOwnable.sol

@@ -0,0 +1,17 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.20;
+
+import {Ownable} from "../../access/Ownable.sol";
+
+contract MyContract is Ownable {
+    constructor(address initialOwner) Ownable(initialOwner) {}
+
+    function normalThing() public {
+        // anyone can call this normalThing()
+    }
+
+    function specialThing() public onlyOwner {
+        // only the owner can call specialThing()!
+    }
+}