bump pgstac image version in validate job

Author: hrodmn

.github/workflows/cicd.yaml

@@ -47,7 +47,7 @@ jobs:
     runs-on: ubuntu-latest
     services:
       pgstac:
-        image: ghcr.io/stac-utils/pgstac:v0.7.10
+        image: ghcr.io/stac-utils/pgstac:v0.8.6
         env:
           POSTGRES_USER: username
           POSTGRES_PASSWORD: password