Updating Old `pandas-stubs` Link in Documentation

[bustosalex1]

I noticed that a link in docs/source/mypy_integration.md was linking to the old VirtusLab pandas-stubs repository that is no longer maintained. This PR updates the link to the newer one that is linked elsewhere in the documentation as well.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.25%. Comparing base (812b2a8) to head (8e09523). Report is 140 commits behind head on main.

:exclamation: There is a different number of reports uploaded between BASE (812b2a8) and HEAD (8e09523). Click for more details.

HEAD has 3 uploads less than BASE

Flag	BASE (812b2a8)	HEAD (8e09523)
	48	45

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1648       +/-   ##
===========================================
- Coverage   94.28%   83.25%   -11.03%     
===========================================
  Files          91      116       +25     
  Lines        7013     8648     +1635     
===========================================
+ Hits         6612     7200      +588     
- Misses        401     1448     +1047     

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[cosmicBboy]

thanks @bustosalex1 ! failing test doesn't seem to be related to this PR, merging now