Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/proxy/UUPSUpgradeableMock.sol

@@ -0,0 +1,33 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../../proxy/utils/UUPSUpgradeable.sol";
+import "../../utils/Counters.sol";
+
+contract NonUpgradeableMock {
+    Counters.Counter internal _counter;
+
+    function current() external view returns (uint256) {
+        return Counters.current(_counter);
+    }
+
+    function increment() external {
+        return Counters.increment(_counter);
+    }
+}
+
+contract UUPSUpgradeableMock is NonUpgradeableMock, UUPSUpgradeable {
+    // Not having any checks in this function is dangerous! Do not do this outside tests!
+    function _authorizeUpgrade(address) internal override {}
+}
+
+contract UUPSUpgradeableUnsafeMock is UUPSUpgradeableMock {
+    function upgradeTo(address newImplementation) public override {
+        ERC1967Upgrade._upgradeToAndCall(newImplementation, bytes(""), false);
+    }
+
+    function upgradeToAndCall(address newImplementation, bytes memory data) public payable override {
+        ERC1967Upgrade._upgradeToAndCall(newImplementation, data, false);
+    }
+}