test_memory_register - Use value that would not be returned on read error

tests/test_memory_register.cpp

@@ -8,7 +8,7 @@
 TEST_CASE("IE controllable via bus")
 {
   u8 test_ram[] = {
-    0x3E, 0xFF, // LD A, $0xFF
+    0x3E, 0xA5, // LD A, $0xA5
     0xE0, 0xFF, // LDH [FF:FF], A
   };
 
@@ -21,5 +21,5 @@ TEST_CASE("IE controllable via bus")
   cpu.step();
   cpu.step();
 
-  CHECK(cpu.state.IE == 0xFF);
+  CHECK(cpu.state.IE == 0xA5);
 }