Fix race condition in tests

test/livebook_web/live/session_live_test.exs

@@ -2122,6 +2122,12 @@ defmodule LivebookWeb.SessionLiveTest do
       # Use the standalone runtime, to encapsulate env var changes
       Session.set_runtime(session.pid, Runtime.Standalone.new())
 
+      # We start the runtime before adding the env var setting,
+      # otherwise a concurrent embedded runtime server could set PATH
+      # in this node and the standalone runtime would inherit it
+      Session.subscribe(session.id)
+      connect_and_await_runtime(session.pid)
+
       separator =
         case :os.type() do
           {:win32, _} -> ";"