fix (Core): use utcfromtimestamp everywhere in Graph instead of fromtimestamp

Author: chaen

src/DIRAC/Core/Utilities/Graphs/GraphData.py

@@ -411,7 +411,7 @@ def initialize(self):
                 self.num_keys.append(next)
                 next += 1
         elif self.key_type == "time":
-            self.num_keys = [date2num(datetime.datetime.fromtimestamp(to_timestamp(key))) for key in self.keys]
+            self.num_keys = [date2num(datetime.datetime.utcfromtimestamp(to_timestamp(key))) for key in self.keys]
         elif self.key_type == "numeric":
             self.num_keys = [float(key) for key in self.keys]