Skip test on macOS

Unable to run GLFW test on macOS CI due to error

> Error #65545 from perl: NSGL: Failed to find a suitable pixel format
> glfwCreateWindow failed, No such file or directory

which is likely due to VM settings.

test.pl

@@ -3,6 +3,9 @@
 # after the test suite so you see something if the build worked.
 #========================================================================
 
+# skip test under under headless macOS
+exit if exists $ENV{CI} and $^O eq 'darwin';
+
 #========================================================================
 # Simple GLFW example
 # Copyright (c) Camilla Berglund <[email protected]>