Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/interfaces/IERC5267.sol

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.9.0) (interfaces/IERC5267.sol)
+
+pragma solidity ^0.8.0;
+
+interface IERC5267 {
+    /**
+     * @dev MAY be emitted to signal that the domain could have changed.
+     */
+    event EIP712DomainChanged();
+
+    /**
+     * @dev returns the fields and values that describe the domain separator used by this contract for EIP-712
+     * signature.
+     */
+    function eip712Domain()
+        external
+        view
+        returns (
+            bytes1 fields,
+            string memory name,
+            string memory version,
+            uint256 chainId,
+            address verifyingContract,
+            bytes32 salt,
+            uint256[] memory extensions
+        );
+}