Bump bockbuild for helpful CI cleaning fix

diff --git a/external/bockbuild b/external/bockbuild
index cc441a606b409159d1704d5ee78c88e06e0d5332..f42561e9ff8e60483897bb54e2191344556de94e 160000 (submodule)
--- a/external/bockbuild
+++ b/external/bockbuild
@@ -1 +1 @@
-Subproject commit cc441a606b409159d1704d5ee78c88e06e0d5332
+Subproject commit f42561e9ff8e60483897bb54e2191344556de94e