fix: make migration 0020 idempotent (check column exists)

alembic/versions/0020_notifications_updated_at.py

@@ -15,15 +15,23 @@ depends_on = None
 
 
 def upgrade() -> None:
-    op.add_column(
+    conn = op.get_bind()
-        "notifications",
+    result = conn.execute(
-        sa.Column(
+        sa.text(
-            "updated_at",
+            "SELECT column_name FROM information_schema.columns "
-            sa.DateTime(timezone=True),
+            "WHERE table_name = 'notifications' AND column_name = 'updated_at'"
-            nullable=False,
+        )
-            server_default=sa.func.now(),
-        ),
     )
+    if result.fetchone() is None:
+        op.add_column(
+            "notifications",
+            sa.Column(
+                "updated_at",
+                sa.DateTime(timezone=True),
+                nullable=False,
+                server_default=sa.func.now(),
+            ),
+        )
 
 
 def downgrade() -> None: