patch 9.1.1492: tests: failure when Wayland compositor fails to start

Problem:  tests: failure when Wayland compositor fails to start
Solution: instead of throwing an error causing a failure, throw
          "Skipped", so that the Vim test suite continues and does not
          fail

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/window_manager.vim b/src/testdir/window_manager.vim
index 39e643e..36fe340 100644
--- a/src/testdir/window_manager.vim
+++ b/src/testdir/window_manager.vim
@@ -42,7 +42,7 @@
 
 func s:StartCompositorExit(job, status)
     if s:wayland_display_name == ""
-      throw "Error: Wayland compositor exited when starting up"
+      throw "Skipped: Error: Wayland compositor exited when starting up"
     endif
 endfunc