Minimize Solidity pragma versions for interface compatibility (#5727)

contracts/token/ERC20/IERC20.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // OpenZeppelin Contracts (last updated v5.1.0) (token/ERC20/IERC20.sol)
 
-pragma solidity ^0.8.20;
+pragma solidity >=0.4.16;
 
 /**
  * @dev Interface of the ERC-20 standard as defined in the ERC.

contracts/token/ERC20/extensions/IERC20Metadata.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // OpenZeppelin Contracts (last updated v5.1.0) (token/ERC20/extensions/IERC20Metadata.sol)
 
-pragma solidity ^0.8.20;
+pragma solidity >=0.6.2;
 
 import {IERC20} from "../IERC20.sol";
 

contracts/token/ERC20/extensions/IERC20Permit.sol

@@ -1,7 +1,7 @@
 // SPDX-License-Identifier: MIT
 // OpenZeppelin Contracts (last updated v5.1.0) (token/ERC20/extensions/IERC20Permit.sol)
 
-pragma solidity ^0.8.20;
+pragma solidity >=0.4.16;
 
 /**
  * @dev Interface of the ERC-20 Permit extension allowing approvals to be made via signatures, as defined in