fix: ensure global devenv symlink exists if removed

[joshuarli]

in the rare event that ~/.local/share/sentry-devenv/bin/devenv (originally installed by install-devenv.sh) is removed, devenv update should restore it

[sentry]

🔍 Existing Issues For Review

Your pull request is modifying functions with the following pre-existing issues:

📄 File: devenv/update.py

Function	Unhandled Issue
main	FileExistsError: [Errno 17] File exists: '/Users/josh/.local/share/sentry-devenv/bin/devenv' -> '/Users/josh/.local/share/sentry-devenv/venv/bin/devenv' ... Event Count: 1

---

_{Did you find this useful? React with a 👍 or 👎}