bug#59742: server-tests failures

[Mattias Engdegård]

The server-tests still fail for an apparent variety of reasons. The behaviour 
differs depending how the test is run: from a terminal, from ´M-x compile`, 
interactively via `M-x ert`, Emacs started with or without `-nw`, and so on.

At least the batch-mode tests would cease failing if we just applied the 
following:

 (defconst server-tests/can-create-frames-p
-  (not (memq system-type '(windows-nt ms-dos)))
+  (and window-system (not (memq system-type '(windows-nt ms-dos))))

Any reason not to?

Even so, there is still a failure if run interactively (M-x ert), and a created 
frame isn't removed properly.