BUG: to_datetime ignores argument combinations

[mroeschke]

• closes BUG: to_datetime with unit mapping ignores utc and box arguments #23760
• closes BUG: to_datetime with unit, utc=True and errors='ignore' does not coerce to UTC #23758
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

[codecov]

Codecov Report

Merging #24407 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24407      +/-   ##
==========================================
+ Coverage    92.3%    92.3%   +<.01%     
==========================================
  Files         163      163              
  Lines       51943    51949       +6     
==========================================
+ Hits        47946    47953       +7     
+ Misses       3997     3996       -1

Flag	Coverage Δ
#multiple	90.71% <100%> (ø)	⬆️
#single	42.99% <40%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/tools/datetimes.py	85.58% <100%> (+0.26%)	⬆️
pandas/util/testing.py	87.84% <0%> (+0.09%)	⬆️

---

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[codecov]

Codecov Report

Merging #24407 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master   #24407      +/-   ##
==========================================
+ Coverage    92.3%    92.3%   +<.01%     
==========================================
  Files         163      163              
  Lines       51943    51949       +6     
==========================================
+ Hits        47946    47953       +7     
+ Misses       3997     3996       -1

Flag	Coverage Δ
#multiple	90.71% <100%> (ø)	⬆️
#single	42.99% <40%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/tools/datetimes.py	85.58% <100%> (+0.26%)	⬆️
pandas/util/testing.py	87.84% <0%> (+0.09%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update fc7bc3f...97c05f3. Read the comment docs.

[jreback]

thanks @mroeschke