Randomize timezone in tests across non-deterministic around 1970 and default

There was some cases when some patches to the datetime code leads to
flaky tests, due to the tests itself had been runned using regular
timezone (TZ).

But if you will this tests with something "specific" (that is not
strictly defined around 1970 year), those tests will fail.

So to catch such issues in the PRs itself, let's randomize
session_timezone as well.

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>

docker/test/stateless/run.sh

@@ -4,6 +4,9 @@
 set -e -x -a
 
 # Choose random timezone for this test run.
+#
+# NOTE: that clickhouse-test will randomize session_timezone by itself as well
+# (it will choose between default server timezone and something specific).
 TZ="$(rg -v '#' /usr/share/zoneinfo/zone.tab  | awk '{print $3}' | shuf | head -n1)"
 echo "Choosen random timezone $TZ"
 ln -snf "/usr/share/zoneinfo/$TZ" /etc/localtime && echo "$TZ" > /etc/timezone

tests/clickhouse-test

@@ -529,6 +529,12 @@ def threshold_generator(always_on_prob, always_off_prob, min_val, max_val):
     return gen
 
 
+# To keep dependency list as short as possible, tzdata is not used here (to
+# avoid try/except block for import)
+def get_localzone():
+    return os.getenv("TZ", "/".join(os.readlink("/etc/localtime").split("/")[-2:]))
+
+
 class SettingsRandomizer:
     settings = {
         "max_insert_threads": lambda: 0
@@ -602,6 +608,19 @@ class SettingsRandomizer:
         "enable_memory_bound_merging_of_aggregation_results": lambda: random.randint(
             0, 1
         ),
+        "session_timezone": lambda: random.choice(
+            [
+                # special non-deterministic around 1970 timezone, see [1].
+                #
+                #   [1]: https://github.com/ClickHouse/ClickHouse/issues/42653
+                "America/Mazatlan",
+                "America/Hermosillo",
+                "Mexico/BajaSur",
+                # server default that is randomized across all timezones
+                # NOTE: due to lots of trickery we cannot use empty timezone here, but this should be the same.
+                get_localzone(),
+            ]
+        ),
     }
 
     @staticmethod