Fix flusight hub formatter

[dylanhmorris]

Checklist

Please:

• Make sure this PR is against "dev", not "main".
• Request a review from one of the current epipredict main reviewers:
  dajmcdon.
• Make sure to bump the version number in DESCRIPTION and NEWS.md.
  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
  0.7.2, then write your changes under the 0.8 heading).
• Consider pinning the epiprocess version in the DESCRIPTION file if
  • You anticipate breaking changes in epiprocess soon
  • You want to co-develop features in epipredict and epiprocess

Change explanations for reviewer

Qualifies the namespace for epidatasets::state_census in two internal functions. The alternative would be to import that name, but qualifying the namespace seems better given that it is only used twice in the codebase.

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

• Resolves epipredict::flusight_hub_formatter() errors without a library(epipredict) call #469

[dajmcdon]

@dylanhmorris Thanks for catching this. It must have been sitting here for a while. Do you need this change on main as well?

[dylanhmorris]

Thanks for the quick review! Would be great to have the patch in main ASAP, but we can point at dev for a bit if necessary.