Fix typos in Datelike impl for DateTime

[ElectrifyPro]

Thanks for contributing to chrono!

If your feature is semver-compatible, please target the 0.4.x branch;
the main branch will be used for 0.5.0 development going forward.

Please consider adding a test to ensure your bug fix/feature will not break in the future.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6ec8f97) 91.69% compared to head (f993d6d) 91.69%.

Additional details and impacted files

@@           Coverage Diff           @@
##            0.4.x    #1376   +/-   ##
=======================================
  Coverage   91.69%   91.69%           
=======================================
  Files          38       38           
  Lines       17608    17608           
=======================================
  Hits        16145    16145           
  Misses       1463     1463           

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[djc]

Thanks!