Explicitly enable postgresql:15 module

Fixes:
Argument 'postgresql' matches 2 streams ('15', '16') of module 'postgresql', but none of the streams are enabled or default
Unable to resolve argument postgresql

containers/Containerfile.c9s

@@ -8,7 +8,7 @@ ENV ANSIBLE_PYTHON_INTERPRETER=/usr/bin/python3 \
 
 RUN dnf -y install epel-release && \
     crb enable && \
-    dnf module enable postgresql -y && \
+    dnf -y module enable postgresql:15 && \
     dnf -y upgrade && \
     dnf -y install ansible python3-pip && \
     dnf clean all