Fix bad HTML filtering regexp (#18339)
Link to issue number:
Closes #17753
Summary of the issue:
The `re_comment` regular expression doesn't account for multi-line HTML
comments.
Description of user facing changes:
None.
Description of developer facing changes:
None.
Description of development approach:
Dismiss code scanning alert, and add explanatory comment
Testing strategy:
CI
Known issues with pull request:
Underlying issue is still present, but not believed to be a problem in our usecase
