Add a weekly regresion test with different Micropython versions (#30)

Don't know which of these will actually work.

.github/workflows/regression_tests.yaml

@@ -0,0 +1,29 @@
+name: "Regression Tests"
+
+on:
+  schedule:
+  - cron: '0 0 * * 0'
+  workflow_dispatch:
+
+jobs:
+  run-tests:
+    strategy:
+      matrix:
+        version: ["v1.17", "v1.18", "v1.23.0", "v1.24.0-preview"]
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.11
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.11'
+    - name: Install dependencies and local packages
+      run: python -m pip install mpremote click
+    - name: Install MicroPython
+      uses: BrianPugh/install-micropython@v2
+      with:
+        reference: ${{ matrix.version }}
+    - name: Install Micropython dependencies
+      run: micropython -m mip install unittest
+    - name: Run tests
+      run: python -m ci.test