Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/token/ERC20FlashMintMock.sol

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../../token/ERC20/extensions/ERC20FlashMint.sol";
+
+abstract contract ERC20FlashMintMock is ERC20FlashMint {
+    uint256 _flashFeeAmount;
+    address _flashFeeReceiverAddress;
+
+    function setFlashFee(uint256 amount) public {
+        _flashFeeAmount = amount;
+    }
+
+    function _flashFee(address, uint256) internal view override returns (uint256) {
+        return _flashFeeAmount;
+    }
+
+    function setFlashFeeReceiver(address receiver) public {
+        _flashFeeReceiverAddress = receiver;
+    }
+
+    function _flashFeeReceiver() internal view override returns (address) {
+        return _flashFeeReceiverAddress;
+    }
+}