Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/mocks/ERC165/ERC165MaliciousData.sol

@@ -0,0 +1,12 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract ERC165MaliciousData {
+    function supportsInterface(bytes4) public pure returns (bool) {
+        assembly {
+            mstore(0, 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff)
+            return(0, 32)
+        }
+    }
+}

backend/lib/openzeppelin-contracts/contracts/mocks/ERC165/ERC165MissingData.sol

@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract ERC165MissingData {
+    function supportsInterface(bytes4 interfaceId) public view {} // missing return
+}

backend/lib/openzeppelin-contracts/contracts/mocks/ERC165/ERC165NotSupported.sol

@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+contract ERC165NotSupported {}

backend/lib/openzeppelin-contracts/contracts/mocks/ERC165/ERC165ReturnBomb.sol

@@ -0,0 +1,18 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../../utils/introspection/IERC165.sol";
+
+contract ERC165ReturnBombMock is IERC165 {
+    function supportsInterface(bytes4 interfaceId) public pure override returns (bool) {
+        if (interfaceId == type(IERC165).interfaceId) {
+            assembly {
+                mstore(0, 1)
+            }
+        }
+        assembly {
+            return(0, 101500)
+        }
+    }
+}