[lldb] Put the new debugger in synchronous mode in TestGlobalModuleCache (llvm#98041)

In async mode, the test terminates sooner than it should
(`run_to_source_breakpoint` does not work in this mode), and then the
test crashes due to llvm#76057. Most of the time, the test does not fail
because its already XFAILed, but the crash still registers as a failure.

Author: labath

lldb/test/API/python_api/global_module_cache/TestGlobalModuleCache.py

@@ -111,6 +111,7 @@ def do_test(self, one_target, one_debugger):
         else:
             if one_target:
                 new_debugger = lldb.SBDebugger().Create()
+                new_debugger.SetAsync(False)
                 self.old_debugger = self.dbg
                 self.dbg = new_debugger