`ECDSA`: Use unchecked arithmetic for the `tryRecover` function (#4301)

Signed-off-by: Pascal Marco Caversaccio <pascal.caversaccio@hotmail.ch>

.changeset/four-adults-knock.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': patch
+---
+
+`ECDSA`: Use unchecked arithmetic for the `tryRecover` function that receives the `r` and `vs` short-signature fields separately.

contracts/utils/cryptography/ECDSA.sol

@@ -98,9 +98,12 @@ library ECDSA {
      * _Available since v4.3._
      */
     function tryRecover(bytes32 hash, bytes32 r, bytes32 vs) internal pure returns (address, RecoverError) {
-        bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
-        uint8 v = uint8((uint256(vs) >> 255) + 27);
-        return tryRecover(hash, v, r, s);
+        unchecked {
+            bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
+            // We do not check for an overflow here since the shift operation results in 0 or 1.
+            uint8 v = uint8((uint256(vs) >> 255) + 27);
+            return tryRecover(hash, v, r, s);
+        }
     }
 
     /**