CI: rebuild libnetconf2-cpp when dependencies change

...because we're pinning this one via that submodule, too.

Change-Id: I8d7f0b48758cb4deb019769eff2ee37224cbe781
Fixes: 337f337 Start building libnetconf2-cpp
diff --git a/ci/build.sh b/ci/build.sh
index 3454392..96a3be1 100755
--- a/ci/build.sh
+++ b/ci/build.sh
@@ -75,7 +75,7 @@
     # persuade BR to rebuild them
     for PROJECT in \
             libyang sysrepo libnetconf2 netopeer2 \
-            libyang-cpp sysrepo-cpp \
+            libyang-cpp sysrepo-cpp libnetconf2-cpp \
             replxx sdbus-cpp \
             ; do
         rm -rf build/{,host-}${PROJECT}-custom/ per-package/{,host-}${PROJECT}/