introduced a ^ in the solidity compiler version

contracts/StakeVault.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 import "./StakeManager.sol";
 import "@openzeppelin/contracts/access/Ownable.sol";

contracts/Token.sol

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: MIT
 
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 import "@openzeppelin/contracts/access/Ownable.sol";
 import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contracts/legacy/Owned.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 /// @dev `Owned` is a base level contract that assigns an `owner` that can be
 ///  later changed
 contract Owned {

contracts/legacy/SNTFaucet.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 import "./SNTPlaceHolder.sol";
 

contracts/legacy/SNTPlaceHolder.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 import "./token/TokenController.sol";
 import "./token/MiniMeToken.sol";
 import "./SafeMath.sol";

contracts/legacy/SafeMath.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 /**
  * Math operations with safety checks

contracts/legacy/optimism/OptimismMintableMiniMeToken.sol

@@ -1,7 +1,7 @@
 
 
 // SPDX-License-Identifier: MIT
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 import { MiniMeToken } from "../token/MiniMeToken.sol";
 import { IERC165 } from "@openzeppelin/contracts/utils/introspection/IERC165.sol";

contracts/legacy/token/ApproveAndCallFallBack.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 abstract contract ApproveAndCallFallBack {
     function receiveApproval(address from, uint256 _amount, address _token, bytes memory _data) virtual public;
 }

contracts/legacy/token/Controlled.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 
 contract Controlled {
     string internal constant ERR_BAD_PARAMETER = "Bad parameter";

contracts/legacy/token/MiniMeToken.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 /*
     Copyright 2016, Jordi Baylina
 

contracts/legacy/token/MiniMeTokenFactory.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 import "./MiniMeToken.sol";
 
 ////////////////

contracts/legacy/token/TokenController.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-3.0
-pragma solidity 0.8.18;
+pragma solidity ^0.8.18;
 /**
  * @dev The token controller contract must implement these functions
  */