Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/interfaces/IERC1363Spender.sol

@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.9.0) (interfaces/IERC1363Spender.sol)
+
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Interface for any contract that wants to support {IERC1363-approveAndCall}
+ * from {ERC1363} token contracts.
+ */
+interface IERC1363Spender {
+    /*
+     * Note: the ERC-165 identifier for this interface is 0x7b04a2d0.
+     * 0x7b04a2d0 === bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))
+     */
+
+    /**
+     * @notice Handle the approval of ERC1363 tokens
+     * @dev Any ERC1363 smart contract calls this function on the recipient
+     * after an `approve`. This function MAY throw to revert and reject the
+     * approval. Return of other than the magic value MUST result in the
+     * transaction being reverted.
+     * Note: the token contract address is always the message sender.
+     * @param owner address The address which called `approveAndCall` function
+     * @param amount uint256 The amount of tokens to be spent
+     * @param data bytes Additional data with no specified format
+     * @return `bytes4(keccak256("onApprovalReceived(address,uint256,bytes)"))`unless throwing
+     */
+    function onApprovalReceived(address owner, uint256 amount, bytes memory data) external returns (bytes4);
+}