Show attribute names in leak tracker

[samtygier-stfc]

Needed for 3.11 classes with lazy dictionaries

Issue

Needed for python 3.11 update ( see #2267 ), but works fine with 3.10

Description

In python 3.11 classes only create the dictionary object if needed ( faster-cpython/ideas#72 ).

When finding owners for objects in the leak tracker, and having an object held by a class like:

class ExampleObject:
    pass

class ExampleContainer:
    def __init__(self, obj):
        self.held_reference = obj

ob1 = ExampleObject()
container = ExampleContainer(ob1)

previously we gc.get_referrers(ob1) would give us the dict (i.e. container.__dict__) and from that we would find the key. Now gc.get_referrers(ob1) gives us the instance, and it is not clear which attribute it is.

The change add a case for a class, and adds the attribute name to extra_info. The act of looking at the __dict__ causes it to be created, so that we can get the name.

Also fix the test class name.

Testing

This fixes the leaktracker test when running with python 3.11 and above

Acceptance Criteria

Tests should pass

Documentation

release notes

[coveralls]

coverage: 73.121% (+0.006%) from 73.115%
when pulling cf19e32 on 2267-leak-tracker
into 8cf298f on main.

[MikeSullivan7]

Using Python 3.12, the error relating to the leak tracker has been fixed and isn't showing anymore. I do get errors relating to mantidimaging/core/data/test/image_stack_test.py::ImageStackTest::test_cant_change_id and mantidimaging/gui/windows/main/test/strictdataset_test.py::StrictDatasetTest::test_cant_change_dataset_id but these are fixed by #2292

[MikeSullivan7]

See comment above!