release: bump version to 1.9.0

[radoering]

Added

• Add an --all-groups option to export dependencies from all groups (#294).

Changed

• Drop support for Python 3.8 (#300).
• Clarify the help text of --with and --only and deprecate --without (#212).
• Fail if the poetry.lock file is not consistent with the pyproject.toml file (#310).

Fixed

• Fix an issue where the export failed with the message "dependency walk failed".
  This fix requires a poetry.lock file created with Poetry 2.x (#286).
• Fix an issue where the pre-commit hook regex matched wrong files (#285).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud