Currently the LibreTranslate web app only shows
the favicon icon when the `LT_WEB=1` environment
variable is set. LT_WEB is used to disable
metadata by default to prevent search engines
from indexing private LibreTranslate instances.
This commit makes the favicon available even when
the metadata is disabled.
- https://github.com/LibreTranslate/LibreTranslate/issues/471