Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/interfaces/IERC5313.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.9.0) (interfaces/IERC5313.sol)
+
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Interface for the Light Contract Ownership Standard.
+ *
+ * A standardized minimal interface required to identify an account that controls a contract
+ *
+ * _Available since v4.9._
+ */
+interface IERC5313 {
+    /**
+     * @dev Gets the address of the owner.
+     */
+    function owner() external view returns (address);
+}