Bug 1757102: Skip test_win32k_enrollment.py for CCov build. r=tjr

CCov builds don't enable the sandbox so win32k test is not relevant.

Differential Revision: https://phabricator.services.mozilla.com/D139707

toolkit/xre/test/marionette/marionette.ini

@@ -1,4 +1,6 @@
 [test_fission_autostart.py]
 [test_win32k_enrollment.py]
-skip-if = os != 'win'
+skip-if =
+  os != 'win'
+  ccov  # Bug 1757102
 [test_exitcode.py]