Allow mini-batching of uncoalesced sparse matrices

[rusty1s]

Fixes #9089

[codecov]

Codecov Report

Attention: Patch coverage is 94.44444% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 89.58%. Comparing base (b678124) to head (70efb06).
Report is 3 commits behind head on master.

Files	Patch %	Lines
torch_geometric/utils/sparse.py	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9099      +/-   ##
==========================================
- Coverage   89.98%   89.58%   -0.41%     
==========================================
  Files         469      470       +1     
  Lines       30135    30160      +25     
==========================================
- Hits        27117    27018      -99     
- Misses       3018     3142     +124     

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