Docker: chmod -R 1777 /tmp sets sticky bit on files

[robertoecf]

Came up in a Gemini code review on our repo.

File: .github/docker/Dockerfile.ci:63

`chmod -R 1777` applies the sticky bit recursively to files inside /tmp — sticky bit only makes sense on directories. Line 61 already handles the directory itself correctly, so this line is doing more harm than good (could hit sockets or pipes if they exist).

Probably just remove the recursive chmod since the directory permission on line 61 is already correct.