Fixed test failure introduced in https://github.com/zopefoundation/ZODB/pull/51

The PR depended on system time being UTC.

src/ZODB/historical_connections.txt

@@ -22,7 +22,8 @@ Historical Connections
     ...     time.time = faux_time_time
     ...     time.sleep = faux_time_sleep
     >>> def utcnow():
-    ...     return datetime.datetime.fromtimestamp(_now)
+    ...     mus = (int(_now % 1 * 1000000), )
+    ...     return datetime.datetime(*time.gmtime(_now)[:6] + mus)
 
 Usage
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