Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/token/ERC20PermitNoRevertMock.sol

@@ -0,0 +1,36 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../../token/ERC20/ERC20.sol";
+import "../../token/ERC20/extensions/draft-ERC20Permit.sol";
+
+abstract contract ERC20PermitNoRevertMock is ERC20Permit {
+    function permitThatMayRevert(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) public virtual {
+        super.permit(owner, spender, value, deadline, v, r, s);
+    }
+
+    function permit(
+        address owner,
+        address spender,
+        uint256 value,
+        uint256 deadline,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    ) public virtual override {
+        try this.permitThatMayRevert(owner, spender, value, deadline, v, r, s) {
+            // do nothing
+        } catch {
+            // do nothing
+        }
+    }
+}