SQLAlchemy 1.4 raises `IntegrityError` here.

It is done.

For bullseye and bookworm the suitename includes `-security` for the
security archive. This suffix has to be removed when using the
override files from ftp-master where the correspondig suites do not
include this suffix.

Closes: #1027804

Closes: #1029497

This makes the generated documentation more useful when working on DAK
itself.

Otherwise flake8 is unhappy about the escape sequence used for Sphinx.

The property returns a `str` as originally intended since
221281b3.

This was suggested by mypy.

This was found by mypy.

This was found by mypy.

This also includes adding more type annotations.

This makes the argument list and type annotations show up in the
documentation generated by Sphinx.