chore(ci): soften plugin-tests xprocess comment

The xprocess theory is plausible but unproven — plugin-shell's python
tests use proc.kill() (SIGKILL only to immediate child, not pgroup) so
a leaked sleep grandchild holding turbo's stdio pipes is equally likely.
Reword the comment so future readers know what evidence we have.

Author: Shaw

.github/workflows/test.yml

@@ -107,10 +107,11 @@ jobs:
       TURBO_TOKEN: ${{ secrets.TURBO_TOKEN }}
       TURBO_TEAM: ${{ vars.TURBO_TEAM }}
       TURBO_REMOTE_ONLY: true
-      # Disable pytest-xprocess globally. Several plugins declare it as a dev
-      # dep but never use it; its session-finalizer leaves orphan child
-      # processes that hold turbo's stdio pipes open after the test passes,
-      # so the job hangs until the 60m wall-clock timeout fires.
+      # Several plugins declare pytest-xprocess as a dev dep but none use it.
+      # Its pytest_terminal_summary hook was the last thing to print before
+      # plugin-tests hung for 33 minutes in run 25234887145, so disable it
+      # globally as a precaution. Safe: `-p no:NAME` is a no-op when NAME
+      # isn't installed.
       PYTEST_ADDOPTS: "-p no:xprocess"
     steps:
       - uses: actions/checkout@v6