Tests: Move image decoder test PNG to its own folder

Author: https://github.com/tcl3
Commit: c62dded5cc
Pull-request: https://github.com/SerenityOS/serenity/pull/21541

Tests/LibGfx/TestImageDecoder.cpp

@@ -85,7 +85,7 @@ TEST_CASE(test_gif)
 
 TEST_CASE(test_not_ico)
 {
-    auto file = MUST(Core::MappedFile::map(TEST_INPUT("buggie.png"sv)));
+    auto file = MUST(Core::MappedFile::map(TEST_INPUT("png/buggie.png"sv)));
     EXPECT(!Gfx::ICOImageDecoderPlugin::sniff(file->bytes()));
     EXPECT(Gfx::ICOImageDecoderPlugin::create(file->bytes()).is_error());
 }
@@ -231,7 +231,7 @@ TEST_CASE(test_pgm)
 
 TEST_CASE(test_png)
 {
-    auto file = MUST(Core::MappedFile::map(TEST_INPUT("buggie.png"sv)));
+    auto file = MUST(Core::MappedFile::map(TEST_INPUT("png/buggie.png"sv)));
     EXPECT(Gfx::PNGImageDecoderPlugin::sniff(file->bytes()));
     auto plugin_decoder = MUST(Gfx::PNGImageDecoderPlugin::create(file->bytes()));