Use ctx.label instead of ctx in progress messages

String representation of ctx will soon be changed, ctx.label should be used
explicitly.

PiperOrigin-RevId: 164016232

tools/build_defs/apple/apple_genrule.bzl

@@ -63,7 +63,7 @@ def _apple_genrule(ctx):
                outputs=list(files_to_build),
                env=env,
                command=argv,
-               progress_message="%s %s" % (message, ctx),
+               progress_message="%s %s" % (message, ctx.label),
                mnemonic="Genrule",
                input_manifests=runfiles_manifests)