CI: start building against CzechLight's br2-external as well

Depends-on: https://cesnet-gerrit-czechlight/c/ci/project-config/+/2558
Depends-on: https://gerrit.cesnet.cz/c/ci/project-config/+/2558
Change-Id: I0ee697498d69727ce2b10ce50f3254198a10ae49
diff --git a/.zuul.CzechLight-internal.yaml b/.zuul.CzechLight-internal.yaml
new file mode 100644
index 0000000..07aa1e8
--- /dev/null
+++ b/.zuul.CzechLight-internal.yaml
@@ -0,0 +1,7 @@
+- project:
+    check:
+      jobs:
+        - czechlight-clearfog:
+            required-projects:
+              - CzechLight/br2-external
+            requires: CzechLight-br2-build-clearfog