chore(release): bump version to 1.6.0

Bump version from 1.5.0 to 1.6.0 in __init__.py and pyproject.toml.
Update test_cli_version_flag to assert against the current package
version instead of a hardcoded string.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "redmine-reporter"
-version = "1.5.0"
+version = "1.6.0"
 description = "Redmine time-entry based issue reporter for internal use"
 readme = "README.md"
 authors = [{ name = "Artem Kokos", email = "artem-kokos@mail.ru" }]