Don't rerun Cirrus CI builds if no relevant files changed

Save CI reruns if only documentation was changed, for example.

.cirrus.yml

@@ -8,6 +8,7 @@ env:
   CCACHE_DIR: /tmp/ccache
 
 task:
+  skip: "changesIncludeOnly('.github/**','docs/**','interface/**','include/wx/{msw,osx,qt}/**','src/{msw,osx,qt}/**')"
   name: Cirrus CI / FreeBSD 13 wxGTK 3
   freebsd_instance:
     image_family: freebsd-13-0