Fix running tests inside of NixOS

[pietroalbini]

The /nix directory not being mounted inside of the container caused inside-docker tests to fail.

[syphar]

I don't know much about nix, or what else could be in there, to see if there might be a security impact where things are exposed to the container that shouldn't.

But shouldn't we add a test? Or do we think it's not necessary?

[pietroalbini]

Oh this is done exclusively during tests, so it doesn't really have a security impact. All packages installed on the host are there.

This is required because on Nix the test binaries's dynamic dependencies are hardcoded paths inside of /nix:

$ ldd target/debug/deps/tests-0bd9ae4af87e59ae
linux-vdso.so.1 (0x00007f04ce6a0000)
libssl.so.3 => /nix/store/8pviily4fgsl02ijm65binz236717wfs-openssl-3.4.1/lib/libssl.so.3 (0x00007f04ce58d000)
libcrypto.so.3 => /nix/store/8pviily4fgsl02ijm65binz236717wfs-openssl-3.4.1/lib/libcrypto.so.3 (0x00007f04cd600000)
libgcc_s.so.1 => /nix/store/7c0v0kbrrdc2cqgisi78jdqxn73n3401-gcc-14.2.1.20250322-lib/lib/libgcc_s.so.1 (0x00007f04cdbd2000)
libm.so.6 => /nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib/libm.so.6 (0x00007f04cd517000)
libc.so.6 => /nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib/libc.so.6 (0x00007f04cd200000)
/nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib/ld-linux-x86-64.so.2 => /nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib64/ld-linux-x86-64.so.2 (0x00007f04ce6a2000)
libdl.so.2 => /nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib/libdl.so.2 (0x00007f04ce586000)
libpthread.so.0 => /nix/store/cg9s562sa33k78m63njfn1rw47dp9z0i-glibc-2.40-66/lib/libpthread.so.0 (0x00007f04ce581000)

[syphar]

Oh this is done exclusively during tests,

Oh I missed that part, too quick to reply , not awake enough yet.