downgrade postgres to 14 cause lack of 15 charm

backend/k8s/db.yaml

@@ -54,7 +54,7 @@ spec:
             claimName: test-observer-db
       containers:
         - name: test-observer-db
-          image: postgres:15.2
+          image: postgres:14
           volumeMounts:
             - name: test-observer-db
               mountPath: /var/lib/postgresql/data

backend/migrations/versions/2023_07_11_1148-158244992900_disallow_multiple_artefact_builds_with_.py

@@ -0,0 +1,32 @@
+"""disallow multiple artefact builds with null revision
+
+Revision ID: 158244992900
+Revises: b33ee8dd41b1
+Create Date: 2023-07-11 11:48:49.777726+00:00
+
+"""
+from alembic import op
+
+
+# revision identifiers, used by Alembic.
+revision = "158244992900"
+down_revision = "6a80dad01d24"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_index(
+        "unique_artefact_build_null_revision",
+        "artefact_build",
+        ["artefact_id", "architecture"],
+        unique=True,
+        postgresql_where=("revision IS NULL"),
+    )
+
+
+def downgrade() -> None:
+    op.drop_index(
+        "unique_artefact_build_null_revision",
+        "artefact_build",
+    )