Doc: fix bogus example about ambiguous timestamps.

I had a brain fade in commit d3289915, and used 2:30AM as the
example timestamp for both spring-forward and fall-back cases.
But it's not actually ambiguous at all in the fall-back case,
because that transition is from 2AM to 1AM under USA rules.
Fix the example to use 1:30AM, which *is* ambiguous.

Noted while answering a question from Aleksander Alekseev.
Back-patch to all supported branches.

Discussion: https://postgr.es/m/2191355.1641828552@sss.pgh.pa.us

doc/src/sgml/datetime.sgml

@@ -210,27 +210,25 @@
    <para>
     Conversely, consider the behavior during a fall-back transition:
 <programlisting>
-=&gt; SELECT '2018-11-04 02:30'::timestamptz;
+=&gt; SELECT '2018-11-04 01:30'::timestamptz;
       timestamptz
 ------------------------
- 2018-11-04 02:30:00-05
+ 2018-11-04 01:30:00-05
 (1 row)
 </programlisting>
-    On that date, there were two possible interpretations of 2:30AM; there
-    was 2:30AM EDT, and then an hour later after the reversion to standard
-    time, there was 2:30AM EST.
+    On that date, there were two possible interpretations of 1:30AM; there
+    was 1:30AM EDT, and then an hour later after clocks jumped back from
+    2AM EDT to 1AM EST, there was 1:30AM EST.
     Again, <productname>PostgreSQL</productname> interprets the given time
-    as if it were standard time (UTC-5).  We can force the matter by
-    specifying daylight-savings time:
+    as if it were standard time (UTC-5).  We can force the other
+    interpretation by specifying daylight-savings time:
 <programlisting>
-=&gt; SELECT '2018-11-04 02:30 EDT'::timestamptz;
+=&gt; SELECT '2018-11-04 01:30 EDT'::timestamptz;
       timestamptz
 ------------------------
- 2018-11-04 01:30:00-05
+ 2018-11-04 01:30:00-04
 (1 row)
 </programlisting>
-    This timestamp could validly be rendered as either 2:30 UTC-4 or
-    1:30 UTC-5; the timestamp output code chooses the latter.
    </para>
 
    <para>