build: Do not install .test files when test is skipped
The skipping introduced in !68 (merged) prevented the executable from being installed but not the .test file that referenced it. This caused installed tests to fail:
Running test: gdk-pixbuf/pixbuf-pixdata.test
Caught exception during testing: Failed to execute child process ?/nix/store/kqmj2776mw24qxyswfbqlmybpws4g4yn-gdk-pixbuf-2.42.2-installedTests/libexec/installed-tests/gdk-pixbuf/pixbuf-pixdata? (No such file or directory)Also, no_resources will never be false as there can never be bmp in enabled_loaders. But I am not sure how to fix that.