BUG: Fix read_csv with index_col

[codingl2k1]

What do these changes do?

Related issue number

Fixes #735

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass

[codecov]

Codecov Report

Merging #736 (51bfe12) into main (771858d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #736   +/-   ##
=======================================
  Coverage   93.54%   93.54%           
=======================================
  Files        1026     1026           
  Lines       79548    79549    +1     
  Branches    16488    16487    -1     
=======================================
+ Hits        74412    74416    +4     
+ Misses       3453     3449    -4     
- Partials     1683     1684    +1     

Flag	Coverage Δ
unittests	93.44% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...hon/xorbits/_mars/dataframe/datasource/read_csv.py	84.82% <100.00%> (+0.96%)	⬆️

... and 12 files with indirect coverage changes

[aresnow1]

LGTM