flake.lock: bump nixpkgs

The current version seems bad, there's a fixed-output derivation
mismatch somewhere in the python tooling:

```
       > error: hash mismatch importing path '/nix/store/c3cjxhn73xa5s8fm79w95d0879bijp04-python3-3.10.13';
       >          specified: sha256:0psh4a7hf891sfc6z38qb3a3jxb1jzljym2kfw3p4i4x409989mr
       >          got:       sha256:1i6kl621m9gm2i2f6p3qm36wqvwh654rfhz0z6hc3fa93a0cngmp
       > copying path '/nix/store/b4fk2q4zn8z1bf9zf19lhf8iygs2z3b7-command-not-found' to 'local'...
```

Signed-off-by: Florian Klink <[email protected]>