Favicon generator: replace realfavicon with favicons package

[isstuev]

Description and Related Issue(s)

resolves #2287

Proposed Changes

[Specify the changes or additions made in this pull request. Please mention if any changes were made to the ENV variables]

Breaking or Incompatible Changes

[Describe any breaking or incompatible changes introduced by this pull request. Specify how users might need to modify their code or configurations to accommodate these changes.]

Additional Information

[Include any additional information, context, or screenshots that may be helpful for reviewers.]

Checklist for PR author

• I have tested these changes locally.
• I added tests to cover any new functionality, following this guide
• Whenever I fix a bug, I include a regression test to ensure that the bug does not reappear silently.
• If I have added, changed, renamed, or removed an environment variable
  • I updated the list of environment variables in the documentation
  • I made the necessary changes to the validator script according to the guide
  • I added "ENVs" label to this pull request