[lldb] Ensure that TestMemoryCache.py reads allocated memory (#151635)

The test reads 400 bytes of memory above the local variable. If the
stack is shallow, this can reach non-allocated space, resulting in a
test failure. The patch fixes the issue by reserving enough space in
the upper stack frame.

Author: igorkudrin

lldb/test/API/functionalities/memory/cache/main.cpp

@@ -1,5 +1,9 @@
-int main ()
-{
-    int my_ints[] = {0x42};
-    return 0; // Set break point at this line.
+int test() {
+  int my_ints[] = {0x42};
+  return 0; // Set break point at this line.
+}
+
+int main() {
+  int dummy[100];
+  return test();
 }