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.

tests/test_cli.py

@@ -127,7 +127,9 @@ def test_cli_version_flag(capsys):
     assert exc_info.value.code == 0
     captured = capsys.readouterr()
     assert "redmine-reporter" in captured.out
-    assert "1.5.0" in captured.out
+    from redmine_reporter import __version__
+
+    assert __version__ in captured.out
 
 
 @mock.patch.dict(os.environ, VALID_ENV, clear=True)