[DEP] deprecate bids_langloc fetcher

[Remi-Gau]

• Closes Datasets fetchers bids_langloc and language_localizer_demo seem to be getting the same data #4216

Changes proposed in this pull request:

• add deprecation warning to the bids_langloc fetcher

[github-actions]

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[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (281656e) 92.07% compared to head (6e7d148) 92.04%.
Report is 3 commits behind head on main.

Files	Patch %	Lines
nilearn/datasets/func.py	63.63%	7 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4219      +/-   ##
==========================================
- Coverage   92.07%   92.04%   -0.04%     
==========================================
  Files         144      144              
  Lines       16374    16407      +33     
  Branches     3428     3431       +3     
==========================================
+ Hits        15077    15102      +25     
- Misses        756      762       +6     
- Partials      541      543       +2     

Flag	Coverage Δ
macos-latest_3.10_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
macos-latest_3.11_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
macos-latest_3.12_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
macos-latest_3.8_test_plotting	91.79% <69.23%> (-0.04%)	⬇️
macos-latest_3.9_test_plotting	91.80% <69.23%> (-0.04%)	⬇️
ubuntu-latest_3.10_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
ubuntu-latest_3.11_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
ubuntu-latest_3.12_test_plotting	91.83% <69.23%> (-0.04%)	⬇️
ubuntu-latest_3.12_test_pre	91.83% <69.23%> (?)
ubuntu-latest_3.8_test_min	68.91% <69.23%> (-0.06%)	⬇️
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ubuntu-latest_3.8_test_plotting	91.79% <69.23%> (-0.04%)	⬇️
ubuntu-latest_3.9_test_plotting	91.80% <69.23%> (-0.04%)	⬇️
windows-latest_3.10_test_plotting	91.81% <69.23%> (-0.04%)	⬇️
windows-latest_3.11_test_plotting	91.81% <69.23%> (-0.04%)	⬇️
windows-latest_3.12_test_plotting	91.81% <69.23%> (-0.04%)	⬇️
windows-latest_3.8_test_plotting	91.77% <69.23%> (-0.04%)	⬇️
windows-latest_3.9_test_plotting	91.78% <69.23%> (-0.04%)	⬇️

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[bthirion]

LGTM, thx !

[ymzayek]

Maybe also add a whatsnew. LGTM otherwise