test(db2): handle TIMESTAMPTZ in test_to_time_column (SQL0180N)

Db2 has no native timezone-aware TIMESTAMP type — TIMESTAMPTZ is mapped to
TIMESTAMP by db2_sqlglot.  CAST('2020-01-01 00:00:00+00:00' AS TIMESTAMP)
is rejected with SQL0180N because Db2 TIMESTAMP literals do not accept a
UTC offset suffix (+00:00).

Fix mirrors the existing Clickhouse guard:
- Strip the +XX:XX offset from the string before calling to_time_column
- Downcast the type to plain TIMESTAMP so to_time_column uses to_ts()
- Add db2 to the TIMESTAMPTZ result dict with no-tz value (same as
  mysql/fabric/spark, which also lack native timezone-aware types)

Author: iawanish

tests/core/engine_adapter/integration/test_integration.py

@@ -2680,6 +2680,7 @@ def test_dialects(ctx: TestContext):
             {
                 "default": pd.Timestamp("2020-01-01 00:00:00+00:00"),
                 "clickhouse": pd.Timestamp("2020-01-01 00:00:00"),
+                "db2": pd.Timestamp("2020-01-01 00:00:00"),
                 "fabric": pd.Timestamp("2020-01-01 00:00:00"),
                 "mysql": pd.Timestamp("2020-01-01 00:00:00"),
                 "spark": pd.Timestamp("2020-01-01 00:00:00"),
@@ -2723,6 +2724,14 @@ def test_to_time_column(
         time_column = re.match(r"^(.*?)\+", time_column).group(1)
         time_column_type = exp.DataType.build("TIMESTAMP('UTC')", dialect="clickhouse")
 
+    if ctx.dialect == "db2" and time_column_type.is_type(exp.DataType.Type.TIMESTAMPTZ):
+        # Db2 has no native timezone-aware TIMESTAMP type (TIMESTAMPTZ maps to TIMESTAMP).
+        # CAST('2020-01-01 00:00:00+00:00' AS TIMESTAMP) is rejected with SQL0180N because
+        # Db2's TIMESTAMP literal format does not accept a UTC offset suffix.
+        # Strip the timezone offset and downcast to plain TIMESTAMP, same approach as Clickhouse.
+        time_column = re.match(r"^(.*?)\+", time_column).group(1)
+        time_column_type = exp.DataType.build("TIMESTAMP")
+
     time_column = to_time_column(time_column, time_column_type, ctx.dialect, time_column_format)
     df = ctx.engine_adapter.fetchdf(exp.select(time_column).as_("the_col"))
     expected = result.get(ctx.dialect, result.get("default"))