Update docker.io/metio/matrix-alertmanager-receiver Docker tag to v2024.8.21

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

@@ -6,7 +6,7 @@
 matrix_alertmanager_receiver_enabled: true
 
 # renovate: datasource=docker depName=docker.io/metio/matrix-alertmanager-receiver
-matrix_alertmanager_receiver_version: 2024.7.3
+matrix_alertmanager_receiver_version: 2024.8.21
 
 matrix_alertmanager_receiver_scheme: https