Update ghcr.io/canonical/charmed-postgresql Docker tag to v14.18 (#983)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

metadata.yaml

@@ -28,7 +28,7 @@ resources:
   postgresql-image:
     type: oci-image
     description: OCI image for PostgreSQL
-    upstream-source: ghcr.io/canonical/charmed-postgresql@sha256:1d771d25f7f29edf5823598eaf33a09dfed4deeb6d86fd9518365de2d577bfb9 # renovate: oci-image tag: 14.17-22.04_edge
+    upstream-source: ghcr.io/canonical/charmed-postgresql@sha256:31fc032a5c4d13a5e0bcac8dbaa40dddbc2568b056708a87df5f7eac6e42e1a7 # renovate: oci-image tag: 14.18-22.04_edge
 
 peers:
   database-peers: