Require Python 3.9

Re spine-tools/Spine-Toolbox#2904

.github/workflows/run_unit_tests.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       matrix:
         os: [windows-latest, ubuntu-22.04]
-        python-version: [3.8, 3.9, "3.10", 3.11, 3.12]
+        python-version: ["3.9", "3.10", "3.11", "3.12"]
     steps:
     - uses: actions/checkout@v4
       with:

README.md

@@ -1,6 +1,6 @@
 # Spine Engine
 
-[![Python](https://img.shields.io/badge/python-3.8%20|%203.9%20|%203.10%20|%203.11|%203.12-blue.svg)](https://www.python.org/downloads/release/python-379/)
+[![Python](https://img.shields.io/badge/python-3.9%20|%203.10%20|%203.11%20|%203.12%20|%203.13-blue.svg)](https://www.python.org/downloads/release/python-379/)
 [![Unit tests](https://github.com/spine-tools/spine-engine/workflows/Unit%20tests/badge.svg)](https://github.com/spine-tools/spine-engine/actions?query=workflow%3A"Unit+tests")
 [![codecov](https://codecov.io/gh/spine-tools/spine-engine/branch/master/graph/badge.svg)](https://codecov.io/gh/spine-tools/spine-engine)
 [![PyPI version](https://badge.fury.io/py/spine-engine.svg)](https://badge.fury.io/py/spine-engine)

pyproject.toml

@@ -11,7 +11,7 @@ classifiers = [
     "License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)",
     "Operating System :: OS Independent",
 ]
-requires-python = ">=3.8.1"
+requires-python = ">=3.9"
 dependencies = [
     "networkx>2.5.1",
     "datapackage>=1.15.2, <1.16",