Updating Juju to use the latest 2.9 version

Change-Id: I7463de831813d92120f0bc959a43140db7cd7332
Signed-off-by: Guillermo Calvino <guillermo.calvino@canonical.com>
diff --git a/requirements.txt b/requirements.txt
index 43624bc..3f53d3c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -39,7 +39,7 @@
     # via kubernetes
 idna==3.3
     # via requests
-juju==2.9.42.2
+juju==2.9.42.4
     # via -r requirements.in
 jujubundlelib==0.5.7
     # via theblues