fix: parse bare date API report times as midnight UTC instead of NA

[JavierMtzRdz]

Checklist

Please:

• Make sure this PR is against "dev", not "main" (unless this is a release
  PR).
• Request a review from one of the current epidatr main reviewers:
  brookslogan, dshemetov, nmdefries, dsweber2.
• Makes sure to bump the version number in DESCRIPTION. Always increment
  the patch version number (the third number), unless you are making a
  release PR from dev to main, in which case increment the minor version
  number (the second number).
• Describe changes made in NEWS.md, making sure breaking changes
  (backwards-incompatible changes to the documented interface) are noted.
  Collect the changes under the next release number (e.g. if you are on
  1.7.2, then write your changes under the 1.8 heading).
• If you changed any vignette (vignettes/*.Rmd.orig), re-knit with make vignettes and commit the regenerated .Rmd files and figures alongside
  the .Rmd.orig sources. See DEVELOPMENT.md.

Change explanations for reviewer

Parse either a date or datetimez from the report_time_column..

Magic GitHub syntax to mark associated Issue(s) as resolved when this is merged into the default branch

• Resolves #{issue number}