debian, setup.py: Add dependency on python3-tomli

Closes: #2169.

python3-coverage >= 6.0 requires python3-tomli to be installed when using
pyproject.toml. There is no hard dependency on tomli for the coverage package
perhaps due to its optional nature.

However, python3-toml is not available in Bullseye. So, require a version of
python3-coverage that does not require python3-tomli.

Tests:

- Run git-pbuilder for stable and unstable. Builds were successful.

- Run autopkgtest for stable and unstable. Dependencies were satisfied but there
was an unrelated error during test collection.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

debian/control

@@ -44,6 +44,8 @@ Build-Depends:
  python3-ruamel.yaml,
  python3-setuptools,
  python3-setuptools-git,
+# python3-tomli is not available in Bullseye
+ python3-tomli | python3-coverage (<< 6.0),
  python3-yaml,
  sshpass,
  xmlto,

debian/tests/control

@@ -14,4 +14,4 @@ Restrictions: needs-root
 # Run unit and integration tests on installed files.
 #
 Test-Command: PYTHONPATH='/usr/lib/python3/dist-packages/plinth/' py.test-3 -p no:cacheprovider --cov=plinth --cov-report=html:debci/htmlcov --cov-report=term
-Depends: git, python3-openssl, python3-pytest, python3-pytest-cov, python3-pytest-django, @
+Depends: git, python3-openssl, python3-pytest, python3-pytest-cov, python3-pytest-django, python3-tomli | python3-coverage (<< 6.0), @

setup.py

@@ -309,6 +309,7 @@ setuptools.setup(
         'pytest-django',
         'flake8',
         'requests',
+        'tomli',
     ],
     package_data={
         '': ['templates/*', 'static/*', 'locale/*/LC_MESSAGES/*.mo']