Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/MulticallTest.sol

@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "./token/ERC20MulticallMock.sol";
+
+contract MulticallTest {
+    function checkReturnValues(
+        ERC20MulticallMock multicallToken,
+        address[] calldata recipients,
+        uint256[] calldata amounts
+    ) external {
+        bytes[] memory calls = new bytes[](recipients.length);
+        for (uint256 i = 0; i < recipients.length; i++) {
+            calls[i] = abi.encodeWithSignature("transfer(address,uint256)", recipients[i], amounts[i]);
+        }
+
+        bytes[] memory results = multicallToken.multicall(calls);
+        for (uint256 i = 0; i < results.length; i++) {
+            require(abi.decode(results[i], (bool)));
+        }
+    }
+}