MAINT: Use .is_monotonic_increasing replace .is_monotonic

[Zeroto521]

• closes #xxxx
• whatsnew entry

.is_monotonic is depracated.

  /home/runner/work/my-data-toolkit/my-data-toolkit/dtoolkit/accessor/series/set_unique_index.py:87: FutureWarning: is_monotonic is deprecated and will be removed in a future version. Use is_monotonic_increasing instead.
    elif not s.index.is_monotonic:

[codecov]

Codecov Report

Merging #749 (e53260c) into main (48c2913) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #749   +/-   ##
=======================================
  Coverage   99.46%   99.46%           
=======================================
  Files         110      110           
  Lines        1500     1500           
  Branches      149      149           
=======================================
  Hits         1492     1492           
  Misses          2        2           
  Partials        6        6           

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

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