test: Avoid resetting mocktime in testing setup

This allows to set the mocktime before the testing setup.

Also, in some fuzz tests the mocktime was reset to 0 before this change,
so set it.

src/test/fuzz/package_eval.cpp

@@ -42,6 +42,7 @@ void initialize_tx_pool()
 {
     static const auto testing_setup = MakeNoLogFileContext<const TestingSetup>();
     g_setup = testing_setup.get();
+    SetMockTime(WITH_LOCK(g_setup->m_node.chainman->GetMutex(), return g_setup->m_node.chainman->ActiveTip()->Time()));
 
     BlockAssembler::Options options;
     options.coinbase_output_script = P2WSH_EMPTY;