Add warning to the docs for start_link_supervised!/2

Author: whatyouhide

lib/ex_unit/lib/ex_unit/callbacks.ex

@@ -612,6 +612,19 @@ defmodule ExUnit.Callbacks do
 
   Note that if the started process terminates before it is linked to the test process,
   this function will exit with reason `:noproc`.
+
+  > #### To Link or Not To Link {: .warning}
+  >
+  > When using `start_link_supervised!/2`, be aware that the order of process termination
+  > during test exit is not guaranteed (for the processes started with
+  > `start_link_supervised!/2`). When the test process exits, the crash signal propagates
+  > to all linked processes virtually simultaneously, which can lead to processes
+  > terminating in an unpredictable order. This is particularly problematic when you have
+  > processes that the test starts with `start_link_supervised!/2` and that depend  on
+  > each other.
+  >
+  > If you need guaranteed shutdown order, use `start_supervised/2`. With that, processes
+  > are shut down *by the test supervisor* in reverse order, ensuring graceful termination.
   """
   @doc since: "1.14.0"
   @spec start_link_supervised!(Supervisor.child_spec() | module | {module, term}, keyword) ::