PR: Update custom button tab index when removing intermediate tabs without changing current selected tab (Widgets)

[dalthviz]

Description of Changes

A tab removal makes the following ones to change their index (<new index> = <old index> - 1). Following that, there is a need to update the index attribute that the custom close button instances have. Otherwise, a IndexError (in the case of the Editor) can be raised. This fix also prevents raising an AttributeError when doing a similar interaction with IPython Console client tabs:

Traceback (most recent call last):
  File "E:\Acer\Documentos\Spyder\spyder\spyder\plugins\ipythonconsole\widgets\main_widget.py", line 1970, in close_client
    if not client.can_close:
AttributeError: 'NoneType' object has no attribute 'can_close'

Issue(s) Resolved

Fixes #22033

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct: dalthviz

[ccordoba12]

Looks good to me, thanks @dalthviz!