Tests/LibGfx: Fix test_not_ico test case

We should expect the sniffing method and the initialize method to fail
because this test case is testing that the ICO image decoder should not
decode random data within it.

Tests/LibGfx/TestImageDecoder.cpp

@@ -58,11 +58,11 @@ TEST_CASE(test_gif)
 TEST_CASE(test_not_ico)
 {
     auto file = Core::MappedFile::map("/res/graphics/buggie.png"sv).release_value();
-    EXPECT_EQ(MUST(Gfx::ICOImageDecoderPlugin::sniff({ (u8 const*)file->data(), file->size() })), true);
+    EXPECT_EQ(MUST(Gfx::ICOImageDecoderPlugin::sniff({ (u8 const*)file->data(), file->size() })), false);
     auto plugin_decoder_or_error = Gfx::ICOImageDecoderPlugin::create({ (u8 const*)file->data(), file->size() });
     EXPECT(!plugin_decoder_or_error.is_error());
     auto plugin_decoder = plugin_decoder_or_error.release_value();
-    EXPECT_EQ(plugin_decoder->initialize(), true);
+    EXPECT_EQ(plugin_decoder->initialize(), false);
 
     EXPECT(plugin_decoder->frame_count());
     EXPECT(!plugin_decoder->is_animated());