fix error message in sparse_check

[araujoms]

There was a typo in sparse_check, that didn't affect the checking but led to a nonsensical error message:

julia> sparse_check(2, [2,1,2], [1], [2])
ERROR: ArgumentError: 1 == colptr[1] != 1

With the PR we get:

julia> sparse_check(2, [2,1,2], [1], [2])
ERROR: ArgumentError: 2 == colptr[1] != 1

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.36%. Comparing base (2b32b60) to head (fcc045c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #681      +/-   ##
==========================================
+ Coverage   84.28%   84.36%   +0.08%     
==========================================
  Files          13       13              
  Lines        9340     9340              
==========================================
+ Hits         7872     7880       +8     
+ Misses       1468     1460       -8     

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