Make royaltyInfo(uint256 _tokenId, uint256 _salePrice) virtual (#3133)

* Make royaltyInfo(uint256 _tokenId, uint256 _salePrice) virtual

Should be cherrypicked in release 4.5

* fix lint

contracts/token/common/ERC2981.sol

@@ -40,7 +40,13 @@ abstract contract ERC2981 is IERC2981, ERC165 {
     /**
      * @inheritdoc IERC2981
      */
-    function royaltyInfo(uint256 _tokenId, uint256 _salePrice) external view override returns (address, uint256) {
+    function royaltyInfo(uint256 _tokenId, uint256 _salePrice)
+        external
+        view
+        virtual
+        override
+        returns (address, uint256)
+    {
         RoyaltyInfo memory royalty = _tokenRoyaltyInfo[_tokenId];
 
         if (royalty.receiver == address(0)) {