fix: add some Linux variables to default passthrough env vars (#10959)
### Description
Adds `XDG_RUNTIME_DIR` to the list of default global pass-through
environment variables. This ensures that the standard XDG runtime
directory is available in tasks by default.
### Testing Instructions
Verify that `XDG_RUNTIME_DIR` is passed through to tasks by running a
Turborepo task that prints its environment variables (e.g., `echo
$XDG_RUNTIME_DIR`).
CLOSES TURBO-4894
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Co-authored-by: Cursor Agent <cursoragent@cursor.com>