Update postgres:16.6-alpine Docker digest to 91e7554 (#44)

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

plausible/docker-compose.yml

@@ -7,7 +7,7 @@ networks:
 services:
   plausible_db:
     restart: unless-stopped
-    image: postgres:16.6-alpine@sha256:52bba373df3c13594014b5e9ccc9f3c2cdb2221d50db1a91ec64570819f18aba
+    image: postgres:16.6-alpine@sha256:91e75546b4f229fa92cec21a2bf831ba03a1c101fc197daafff657f153e93a39
     volumes:
       - /home/aosus/plausible/postgres:/var/lib/postgresql/data
     environment: