fix python 3.12 utcnow() deprecation warning

Warning is:

/usr/lib64/python3.12/site-packages/ifcopenshell/api/project/create_file.py:61:
DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version.
Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).

src/blenderbim/blenderbim/bim/export_ifc.py

@@ -74,7 +74,7 @@ class IfcExporter:
     def set_header(self):
         self.file.wrapped_data.header.file_name.name = os.path.basename(self.ifc_export_settings.output_file)
         self.file.wrapped_data.header.file_name.time_stamp = (
-            datetime.datetime.utcnow()
+            datetime.datetime.now(datetime.UTC)
             .replace(tzinfo=datetime.timezone.utc)
             .astimezone()
             .replace(microsecond=0)

src/ifcopenshell-python/ifcopenshell/api/project/create_file.py

@@ -58,7 +58,7 @@ class Usecase:
         self.file = ifcopenshell.file(schema=self.settings["version"])
         self.file.wrapped_data.header.file_name.name = "/dev/null"  # Hehehe
         self.file.wrapped_data.header.file_name.time_stamp = (
-            datetime.datetime.utcnow()
+            datetime.datetime.now(datetime.UTC)
             .replace(tzinfo=datetime.timezone.utc)
             .astimezone()
             .replace(microsecond=0)