Fix README badges (#33)

mysql-router badge: point to DPE track instead of 8.0 track
ci.yaml badge: update default branch name

Author: carlcsaposs-canonical

README.md

@@ -1,8 +1,8 @@
 # mysql-router-operators
 [![Charmhub](https://charmhub.io/mysql-router-k8s/badge.svg)](https://charmhub.io/mysql-router-k8s)
-[![Charmhub](https://charmhub.io/mysql-router/badge.svg)](https://charmhub.io/mysql-router)
+[![Charmhub](https://charmhub.io/mysql-router/badge.svg?channel=dpe/candidate)](https://charmhub.io/mysql-router)
 [![Release](https://github.com/canonical/mysql-router-operators/actions/workflows/release.yaml/badge.svg)](https://github.com/canonical/mysql-router-operators/actions/workflows/release.yaml)
-[![Tests](https://github.com/canonical/mysql-router-operators/actions/workflows/ci.yaml/badge.svg?branch=main)](https://github.com/canonical/mysql-router-operators/actions/workflows/ci.yaml)
+[![Tests](https://github.com/canonical/mysql-router-operators/actions/workflows/ci.yaml/badge.svg?branch=dpe)](https://github.com/canonical/mysql-router-operators/actions/workflows/ci.yaml)
 -----------------
 ## Description