On Debian 11 (bullseye) with Python 3 the test otherwise failed
with SQLAlchemy complaining:
```
    TypeError: Incompatible collection type: dict_values is not list-like
```

The condition was always true as `binaries` and `sources` are query
objects and not lists.  We only want to update `last_changed` when
either query actually returned something.

This addresses warnings that debhelper compat level 9 is deprecated in
newer debhelper versions.

The interface changed in incompatible ways between Debian 10 (buster)
and Debian bullseye.

There are incompatible changes in some Python modules that make the
tests fail. As it is a new test, allow the failure until this is
fixed.

Some Python 2 modules no longer exist in Debian bullseye, so trying to
satisfy all build-dependencies in d/control would fail there.  For now
just install them in `run-ci` where we can modify the list of package
to install dynamically.

This way we can also run Python 3 tests in parallel without requiring
more resources in total.

Otherwise if one accepts multiple uploads in `dak process-new`, but
only edits the `COMMENTS` file for one `.changes` file one would end
up accepting an upload into a public suite.  This would be a problem
for uploads fixing embargoed issues.

4800f574 was a bit too enthusiastic
with removing executable bits.

This prevents encoding errors with python2.

It is no longer executable.

These are displayed during new processing.

The subprocess module has been unused since 400066ea
(daklib/rm.py: format date in python).

Fixes:

    daklib/architecture.py:113: SyntaxWarning: "is" with a literal. Did you mean "=="?

with Python >= 3.8.

It looks like some removal records had trailing whitespace which
confuses users of the deb822 file.

Reference: https://bugs.debian.org/960504

This reverts commit e43911e2.