refactor: change pragma to ">=0.8.18"

.solhint.json

@@ -2,7 +2,7 @@
   "extends": "solhint:recommended",
   "rules": {
     "code-complexity": ["error", 8],
-    "compiler-version": ["error", ">=0.8.4"],
+    "compiler-version": ["error", ">=0.8.18"],
     "func-name-mixedcase": "off",
     "func-visibility": ["error", { "ignoreConstructors": true }],
     "max-line-length": ["error", 120],

script/Foo.s.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: UNLICENSED
-pragma solidity >=0.8.4;
+pragma solidity >=0.8.18;
 
 import { Script } from "forge-std/Script.sol";
 import { Foo } from "../src/Foo.sol";

src/Foo.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: UNLICENSED
-pragma solidity >=0.8.4;
+pragma solidity >=0.8.18;
 
 contract Foo {
 // solhint-disable-previous-line no-empty-blocks

test/Foo.t.sol

@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: UNLICENSED
-pragma solidity >=0.8.4;
+pragma solidity >=0.8.18;
 
 import { PRBTest } from "@prb/test/PRBTest.sol";
 import { console2 } from "forge-std/console2.sol";