ci: update Forgejo workflow

Run the python tests in a Python container using a custom local action
and a Dockerfile to build the testing environment.

Resolves the issue where setup-python doesn't seem to work with Forgejo
actions (at least for me anyway).

.forgejo/actions/python/Dockerfile

@@ -0,0 +1,5 @@
+FROM python:3.12.5
+
+ADD *.sh /
+
+ENTRYPOINT ["/entrypoint.sh"]

.forgejo/actions/python/action.yaml

@@ -0,0 +1,5 @@
+name: "Run Python Tests"
+description: "Runs the Python Tests"
+runs:
+  using: "docker"
+  image: "Dockerfile"

.forgejo/actions/python/entrypoint.sh

@@ -0,0 +1,6 @@
+#!/bin/sh
+
+set -e
+
+python3 -V
+python3 tests.py

.forgejo/workflows/workflow.yaml

@@ -13,10 +13,6 @@ jobs:
     runs-on: docker
     steps:
     - name: Checkout Repository
-      uses: https://code.forgejo.org/actions/checkout@v3
-    - name: Install Python 3
-      uses: https://github.com/actions/setup-python@v5
-      with:
-        python-version: '3.12.2'
+      uses: https://code.forgejo.org/actions/checkout@v4
     - name: Test Code
-      run: python tests.py
+      uses: ./.forgejo/actions/python