[ZCash] Disable ZCashShieldSyncServiceTest::ScanBlocks on MacOs (#27815)

Resolves https://github.com/brave/brave-browser/issues/44241

components/brave_wallet/browser/zcash/zcash_shield_sync_service_unittest.cc

@@ -245,6 +245,12 @@ class ZCashShieldSyncServiceTest : public testing::Test {
   base::test::TaskEnvironment task_environment_;
 };
 
+#if defined(IS_MAC)
+#define MAYBE_ScanBlocks DISABLED_ScanBlocks
+#else
+#define MAYBE_ScanBlocks ScanBlocks
+#endif
+
 TEST_F(ZCashShieldSyncServiceTest, ScanBlocks) {
   auto mock_block_scanner = CreateMockOrchardBlockScannerProxy();