Fix PR Env description update race condition

[doshitan]

Context

bin/{update,destroy}-pr-environment scripts ultimately just call gh pr edit to update the PR description to add or remove the link to the environment for each app. If multiple apps are being deployed/destroyed at the same time, some of those PR description updates will be missed.

Example: navapbc/platform-test#241

https://github.com/navapbc/platform-test/actions/runs/19515689421/job/55866704034

Instructions

There could be multiple approaches:

1. Add some locking/concurrency control around the PR description update part, maybe:
   • Split out the gh pr edit call into a separate script
   • Have the CI actions call the edit script to a separate step/job that has a different concurrency setting?
2. Change set up to post/edit a comment on the PR for each app environment

Success criteria

PR environment creation and deletion are always captured in PR.