Fix .gitignore: stop tracking ignored files

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

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.9.0) (governance/extensions/GovernorVotes.sol)
+
+pragma solidity ^0.8.0;
+
+import "../Governor.sol";
+import "../../interfaces/IERC5805.sol";
+
+/**
+ * @dev Extension of {Governor} for voting weight extraction from an {ERC20Votes} token, or since v4.5 an {ERC721Votes} token.
+ *
+ * _Available since v4.3._
+ */
+abstract contract GovernorVotes is Governor {
+    IERC5805 public immutable token;
+
+    constructor(IVotes tokenAddress) {
+        token = IERC5805(address(tokenAddress));
+    }
+
+    /**
+     * @dev Clock (as specified in EIP-6372) is set to match the token's clock. Fallback to block numbers if the token
+     * does not implement EIP-6372.
+     */
+    function clock() public view virtual override returns (uint48) {
+        try token.clock() returns (uint48 timepoint) {
+            return timepoint;
+        } catch {
+            return SafeCast.toUint48(block.number);
+        }
+    }
+
+    /**
+     * @dev Machine-readable description of the clock as specified in EIP-6372.
+     */
+    // solhint-disable-next-line func-name-mixedcase
+    function CLOCK_MODE() public view virtual override returns (string memory) {
+        try token.CLOCK_MODE() returns (string memory clockmode) {
+            return clockmode;
+        } catch {
+            return "mode=blocknumber&from=default";
+        }
+    }
+
+    /**
+     * Read the voting weight from the token's built in snapshot mechanism (see {Governor-_getVotes}).
+     */
+    function _getVotes(
+        address account,
+        uint256 timepoint,
+        bytes memory /*params*/
+    ) internal view virtual override returns (uint256) {
+        return token.getPastVotes(account, timepoint);
+    }
+}