Updated Group.c to correct bug with insert into displayio.Group

[kmatch98]

This is to resolve the bug when inserting an element at the end of an existing group. See issue: #3129 (comment)

In this PR, per your suggestions I check if the requested insert index is equal to the length of the group. If so, then call append, else call insert.

I hunted around the code for the proper type conversions, but I am unsure if I am doing the type conversion correctly.
** Please double-check since I am not familiar with any of the data types that are used here.

I built this and verified on an Itsy-Bitsy NRF52840

Here is how I verified the code:

>>> 
>>> import displayio
>>> group1=displayio.Group(max_size=5)
>>> group2=displayio.Group(max_size=5)
>>> group3=displayio.Group(max_size=5)
>>> group1.insert(0,group2)
>>> group1.insert(1,group3)
>>> len(group1)
2
>>> group1.pop(0)
<Group>
>>> len(group1)
1
>>> group1.insert(1,group2)
>>> len(group1)
2
>>> 

@FoamyGuy whenever this bug is corrected, you can simplify the workaround to the label.py related where you had to double-check the length of the group to decide whether to use group.append or group.insert.

[FoamyGuy]

I tested this out on a PyGamer. Prior to these changes I get IndexError from this line group1.insert(0,group2). With these changes it is working successfully.

Thank you @kmatch98 for working on this! It will be great to unwind this bit of complexity in display_text

[tannewt]

Please delete the mpy-cross file. The easiest way is to edit the existing commit to remove the file.

This fix looks good otherwise! Just a style comment. Thanks!

[tannewt]

Thank you!