chore: update charm definitions to support Juju 4.0

Author: Ninfa-Jeon

charms/k8s-charm/charmcraft.yaml

@@ -16,7 +16,7 @@ links:
 assumes:
   - k8s-api
   - juju >= 3.6
-  - juju < 4.0
+  - juju < 5.0
 base: ubuntu@24.04
 platforms:
   amd64:

charms/machine-charm/charmcraft.yaml

@@ -15,7 +15,7 @@ links:
   documentation: https://discourse.charmhub.io/t/juju-dashboard-docs-index/10772
 assumes:
   - juju >= 3.6
-  - juju < 4.0
+  - juju < 5.0
 base: ubuntu@24.04
 platforms:
   amd64: