Fixed #34955 -- Made Concat() use || operator on PostgreSQL.

This also avoids casting string based expressions in Concat() on
PostgreSQL.

tests/db_functions/text/test_concat.py

@@ -75,7 +75,10 @@ class ConcatTests(TestCase):
         expected = article.title + " - " + article.text
         self.assertEqual(expected.upper(), article.title_text)
 
-    @skipUnless(connection.vendor == "sqlite", "sqlite specific implementation detail.")
+    @skipUnless(
+        connection.vendor in ("sqlite", "postgresql"),
+        "SQLite and PostgreSQL specific implementation detail.",
+    )
     def test_coalesce_idempotent(self):
         pair = ConcatPair(V("a"), V("b"))
         # Check nodes counts
@@ -89,3 +92,18 @@ class ConcatTests(TestCase):
         qs = Article.objects.annotate(description=Concat("title", V(": "), "summary"))
         # Multiple compilations should not alter the generated query.
         self.assertEqual(str(qs.query), str(qs.all().query))
+
+    def test_concat_non_str(self):
+        Author.objects.create(name="The Name", age=42)
+        with self.assertNumQueries(1) as ctx:
+            author = Author.objects.annotate(
+                name_text=Concat(
+                    "name", V(":"), "alias", V(":"), "age", output_field=TextField()
+                ),
+            ).get()
+        self.assertEqual(author.name_text, "The Name::42")
+        # Only non-string columns are casted on PostgreSQL.
+        self.assertEqual(
+            ctx.captured_queries[0]["sql"].count("::text"),
+            1 if connection.vendor == "postgresql" else 0,
+        )