test: Skip WalletTests.WalletNetworkSerialization

It suffers from a race condition when `zcash-gtest` runs tests in
parallel, because it depends on the global network parameters being
stable across the whole test. Other tests changing the parameters from
underneath it cause the test to fail in weird and wonderful ways.

src/wallet/gtest/test_wallet.cpp

@@ -138,6 +138,7 @@ TEST(WalletTests, SetupDatadirLocationRunAsFirstTest) {
 }
 
 TEST(WalletTests, WalletNetworkSerialization) {
+    GTEST_SKIP() << "Skipping because it has a race condition and cannot be run in parallel.";
     SelectParams(CBaseChainParams::TESTNET);
 
     // Get temporary and unique path for file.