Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/token/ERC1155/extensions/ERC1155Pausable.sol

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+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts (last updated v4.8.2) (token/ERC1155/extensions/ERC1155Pausable.sol)
+
+pragma solidity ^0.8.0;
+
+import "../ERC1155.sol";
+import "../../../security/Pausable.sol";
+
+/**
+ * @dev ERC1155 token with pausable token transfers, minting and burning.
+ *
+ * Useful for scenarios such as preventing trades until the end of an evaluation
+ * period, or having an emergency switch for freezing all token transfers in the
+ * event of a large bug.
+ *
+ * IMPORTANT: This contract does not include public pause and unpause functions. In
+ * addition to inheriting this contract, you must define both functions, invoking the
+ * {Pausable-_pause} and {Pausable-_unpause} internal functions, with appropriate
+ * access control, e.g. using {AccessControl} or {Ownable}. Not doing so will
+ * make the contract unpausable.
+ *
+ * _Available since v3.1._
+ */
+abstract contract ERC1155Pausable is ERC1155, Pausable {
+    /**
+     * @dev See {ERC1155-_beforeTokenTransfer}.
+     *
+     * Requirements:
+     *
+     * - the contract must not be paused.
+     */
+    function _beforeTokenTransfer(
+        address operator,
+        address from,
+        address to,
+        uint256[] memory ids,
+        uint256[] memory amounts,
+        bytes memory data
+    ) internal virtual override {
+        super._beforeTokenTransfer(operator, from, to, ids, amounts, data);
+
+        require(!paused(), "ERC1155Pausable: token transfer while paused");
+    }
+}