Several years ago, during a Django upgrade, we updated the extension

static media template tag code to correctly join strings together for

loading bundles, using format_html_join instead of naively joining

strings. This was commit 080996bf0.
Part of this involved yielding tuples in a generator, but we missed some

yields. When using include_bundles, we ended up yielding strings and

not tuples of strings, and this broke the process by which they were

joined.
This fixes that issue, and adds type safety throughout the template tag

code.
Unit tests have also been updated to cover include_bundles, so it

doesn't regress.

Unit tests and type checkers pass.