devenv: fix overwriting read-only .pth file when dependencies change

This update fixes the following error:

    --- devenv:python:poetry failed with error: Task exited with status: exit status: 1
    --- devenv:python:poetry stdout:
    0001.44: ~/devel/git/github.com/onekey-sec/unblob ~/devel/git/github.com/onekey-sec/unblob
    0000.23: Installing dependencies from lock file
    0000.07:
    0000.07: No dependencies to install or update
    0000.07:
    0000.07: Installing the current project: unblob (24.9.30)
    --- devenv:python:poetry stderr:
    0000.00: cp: cannot create regular file '.venv/lib/python3.12/site-packages/devenv.pth': Permission denied

We are creating a symlink to the nix-store instead of copying a
read-only file.

---

Flake lock file updates:

• Updated input 'devenv':
    'github:vlaci/devenv/385d38cfb6872e7f95cae30d94f7fc4afd23fd76' (2024-10-30)
  → 'github:vlaci/devenv/4caf75b37c5d633fde612cd52bb794bcbf75d24a' (2024-11-12)