EHN: drop_inf's inf option supports + and -

[Zeroto521]

• closes #xxxx
• whatsnew entry

[codecov]

Codecov Report

Merging #539 (840d744) into main (d667a7b) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #539      +/-   ##
==========================================
- Coverage   99.63%   99.63%   -0.01%     
==========================================
  Files          60       60              
  Lines         824      816       -8     
  Branches       92       89       -3     
==========================================
- Hits          821      813       -8     
  Misses          1        1              
  Partials        2        2              

Impacted Files	Coverage Δ
dtoolkit/accessor/_util.py	100.00% <100.00%> (ø)
dtoolkit/accessor/dataframe/drop_inf.py	100.00% <100.00%> (ø)
dtoolkit/accessor/series/drop_inf.py	100.00% <100.00%> (ø)

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