Fix broken `firing` template for matrix-alertmanager-receiver

This was an upstream documentation mistake that propagated to us
during the update in 25e7cac28d.

The upstream fix is here:

- 8f7f4d1dd1
- https://github.com/metio/matrix-alertmanager-receiver/pull/99

roles/custom/matrix-alertmanager-receiver/defaults/main.yml

@@ -168,7 +168,7 @@ matrix_alertmanager_receiver_config_templating_firing_template: |-
   {{ else if eq .Alert.Labels.severity "critical" }}
   {{ $color = "red" }}
   {{ end }}
-  {{ if eq .Alert.status "resolved" }}
+  {{ if eq .Alert.Status "resolved" }}
   {{ $color = "green" }}
   {{ end }}
   <p>