test: disable test_wtf of datalad-core-4

This commit disables the test
`datalad.locals.tests.test_wtf.test_wtf`.
It fails due to an error in datalad, see
this issue:
<datalad/datalad#7627>
and the corresponding PR:
<datalad/datalad#7628>.

Once the PR datalad #7628 is merged this commit can
be reverted.

.appveyor.yml

@@ -205,6 +205,8 @@ environment:
     - job_name: datalad-core-4
       DTS: >
         datalad.local
+      KEYWORDS: >
+        not test_wtf
       APPVEYOR_BUILD_WORKER_IMAGE: Ubuntu2004
       PY: 3.8
       INSTALL_SYSPKGS: