Fix for as.IDate() to retain names even before some as.Date() calls did so in R (4.1.2)

[MichaelChirico]

Follow-up to #7800 for pre-R-4.1.2 behavior of as.Date.POSIXlt.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (dcaa87c) to head (9888866).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7850   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          88       88           
  Lines       17286    17286           
=======================================
  Hits        17116    17116           
  Misses        170      170           

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[github-actions]

• HEAD=as-date-names-old-r much slower for as.data.table.array improved in #7019
  

Generated via commit 9888866

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	2 minutes and 49 seconds
Installing different package versions	1 minutes and 34 seconds
Running and plotting the test cases	6 minutes and 29 seconds