Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/governance/extensions/IGovernorTimelock.sol

@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts v4.4.1 (governance/extensions/IGovernorTimelock.sol)
+
+pragma solidity ^0.8.0;
+
+import "../IGovernor.sol";
+
+/**
+ * @dev Extension of the {IGovernor} for timelock supporting modules.
+ *
+ * _Available since v4.3._
+ */
+abstract contract IGovernorTimelock is IGovernor {
+    event ProposalQueued(uint256 proposalId, uint256 eta);
+
+    function timelock() public view virtual returns (address);
+
+    function proposalEta(uint256 proposalId) public view virtual returns (uint256);
+
+    function queue(
+        address[] memory targets,
+        uint256[] memory values,
+        bytes[] memory calldatas,
+        bytes32 descriptionHash
+    ) public virtual returns (uint256 proposalId);
+}