private static String readFile(final Path file) {
        try {
            return Files.readString(file);
        } catch (final IOException e) {
            throw new RuntimeException(e);
        }
    }
This is {@link CheckAsyncAnnotationInInterface}.
Fail build if Async annotation is not in an interface.
This ensures interface exists for Async classes so Spring can use JDK proxy instead of cglib proxy.
@author Hal Deadman
@since 6.5.0
ci/checks/CheckAsyncAnnotationInInterface.java