Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/test/helpers/time.js

@@ -0,0 +1,17 @@
+const ozHelpers = require('@openzeppelin/test-helpers');
+const helpers = require('@nomicfoundation/hardhat-network-helpers');
+
+module.exports = {
+  clock: {
+    blocknumber: () => helpers.time.latestBlock(),
+    timestamp: () => helpers.time.latest(),
+  },
+  clockFromReceipt: {
+    blocknumber: receipt => Promise.resolve(receipt.blockNumber),
+    timestamp: receipt => web3.eth.getBlock(receipt.blockNumber).then(block => block.timestamp),
+  },
+  forward: {
+    blocknumber: ozHelpers.time.advanceBlockTo,
+    timestamp: helpers.time.increaseTo,
+  },
+};