[emergency revert]: make pname nix once more

Embarrassingly, I submitted a CL overriding submit requirements since
I thought it was spurious failures. However, the CI failure was in fact
real, and I have hopefully learned my lesson. The CI failure is that:

```
vm-test-run-nix-upgrade-nix> machine # installing 'nix-2.18.1'
vm-test-run-nix-upgrade-nix> machine # building '/nix/store/2b6fdf7wvahd00bg2ff0393bhd597a0h-user-environment.drv'...
vm-test-run-nix-upgrade-nix> machine # error: Unable to build profile. There is a conflict for the following files:
vm-test-run-nix-upgrade-nix> machine #
vm-test-run-nix-upgrade-nix> machine #          /nix/store/dn6mhhr92bh3ad0n4pd1538ww88khjii-nix-2.18.1/lib/libboost_context.so
vm-test-run-nix-upgrade-nix> machine #          /nix/store/w4vffn9iq0znk8bcg5i2giij90xy6db6-lix-2.90.0pre20240523_c97e171/lib/libboost_context.so
vm-test-run-nix-upgrade-nix> machine # error: builder for '/nix/store/2b6fdf7wvahd00bg2ff0393bhd597a0h-user-environment.drv' failed with exit code 1
vm-test-run-nix-upgrade-nix> machine # error: program '/nix/store/w4vffn9iq0znk8bcg5i2giij90xy6db6-lix-2.90.0pre20240523_c97e171/bin/nix-env' failed with exit code 100
```

This is definitely caused by the pname not being the same, so we had
better revert that part of the change until we know we won't regress
anything by doing this.

Fixes: https://gerrit.lix.systems/c/lix/+/1152/5
Change-Id: I0e9d573987f2819c106fb7cea87410fa75152274

package.nix

@@ -49,7 +49,7 @@
   # internal fork of nix-doc providing :doc in the repl
   lix-doc ? __forDefaults.lix-doc,
 
-  pname ? "lix",
+  pname ? "nix",
   versionSuffix ? "",
   officialRelease ? false,
   # Set to true to build the release notes for the next release.