lnprototest: update version to fix flake issues.

rustyrussell · cdecker · commit 78a48fa7ec84 · 2021-08-16T10:50:22.000+02:00
See rustyrussell/lnprototest#20 Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/external/lnprototest b/external/lnprototest
@@ -1 +1 @@
-Subproject commit 2b99492ed0544a6c0475a79ca4ed484bc9191635
+Subproject commit 9beb1677d61534a34a4ab365cb79b84376b549fc
