nixguix: Make nar ignore .hg and .svn folders as well

This aligns further with the guix hash command behavior.

```
$ guix hash -S nar -f base32 -H sha256 -x /var/tmp/panda
apq7sedacxf2lqaebllbngtszci63v7cbwxmo4276k26nv4ocseq
$ python -m nar -f base32 -H sha256 /var/tmp/panda
apq7sedacxf2lqaebllbngtszci63v7cbwxmo4276k26nv4ocseq====
guix hash -S nar -f base32 -H sha256 -x /var/tmp/hgview
lepywr37sfg4uqmetcww2q2hxjicgags3xt5fjbvjoepiqcluj5q
$ python -m nar -f base32 -H sha256 /var/tmp/hgview
lepywr37sfg4uqmetcww2q2hxjicgags3xt5fjbvjoepiqcluj5q====
```

Related to T4538#93319