This was broken by 7a029caa

We can not use `ByteString.pack` and then print it as `String`, which
will get encoded again based on the system setting, and very likely,
we get different things unless the encoding is something like ISO-8859-1, e.g.
in UTF-8 environment, the magic of gz "\x1f\x8b" will get encoded again
into "\x1f\xc2\x8b".

Before:

```
$ /cabal sdist --output-dir=- | tar -t -z -f -
tar: This does not look like a tar archive
```

And now:

```
$ cabal sdist --output-dir=- | tar -t -z -f -  | tail -n 1
cabal-install-2.5.0.0/tests/README.md
```