Update docker.io/library/postgres Docker tag to v13.21

Author: renovate[bot]

compose.yaml

@@ -124,7 +124,7 @@ services:
       retries: 20
 
   liminator-db:
-    image: docker.io/library/postgres:13.10
+    image: docker.io/library/postgres:13.21
     environment:
       - POSTGRES_DB=liminator
       - POSTGRES_USER=vality
@@ -147,7 +147,7 @@ services:
       retries: 10
 
   shumway-db:
-    image: docker.io/library/postgres:13.10
+    image: docker.io/library/postgres:13.21
     environment:
       - POSTGRES_DB=shumway
       - POSTGRES_USER=postgres