ci(postgres): pin testcontainer to postgres:16-alpine

The introspection query in `fetch_columns` reads
`pg_attribute.attgenerated` (added in PG 12) to detect generated
columns. testcontainers-modules' default tag for `Postgres::default()`
is older than 12, so since the DDL UI feature landed every CI run
has failed with `column a.attgenerated does not exist (SQLSTATE 42703)`.

Pin the test container to 16-alpine. PostgreSQL 11 hit upstream EOL
in November 2023, so requiring 12+ is reasonable for production
deployments; not worth the per-version dialect branching to
remain compatible with EOL versions.

Author: datlechin

linux/crates/drivers/postgres/tests/integration.rs

@@ -8,11 +8,21 @@ use uuid::Uuid;
 use drivers_postgres::PgDriver;
 use tablepro_core::{ConnectOptions, Connection, DatabaseDriver, Value};
 use testcontainers::ContainerAsync;
+use testcontainers::ImageExt;
 use testcontainers_modules::postgres::Postgres;
 use testcontainers_modules::testcontainers::runners::AsyncRunner;
 
 async fn start_pg() -> (ContainerAsync<Postgres>, ConnectOptions) {
-    let container = Postgres::default().start().await.expect("start postgres container");
+    // Pin to Postgres 16: the introspection query in `fetch_columns`
+    // reads `pg_attribute.attgenerated`, which was added in PG 12.
+    // testcontainers-modules's default tag is older and breaks the
+    // generated-column flag query. PG 11 hit upstream EOL in Nov 2023
+    // so production deployments shouldn't be older than this anyway.
+    let container = Postgres::default()
+        .with_tag("16-alpine")
+        .start()
+        .await
+        .expect("start postgres container");
     let host = container.get_host().await.expect("host").to_string();
     let port = container.get_host_port_ipv4(5432).await.expect("port");
     let opts = ConnectOptions {