update to Python 3.12 for running tests

Author: dhalbert

.github/workflows/run-tests.yml

@@ -16,7 +16,7 @@ jobs:
         test: [all, mpy, native, native_mpy]
     env:
       CP_VERSION: ${{ inputs.cp-version }}
-      MICROPY_CPYTHON3: python3.8
+      MICROPY_CPYTHON3: python3.12
       MICROPY_MICROPYTHON: ../ports/unix/build-coverage/micropython
       TEST_all:
       TEST_mpy: --via-mpy -d basics float micropython
@@ -32,7 +32,7 @@ jobs:
     - name: Set up python
       uses: actions/setup-python@v5
       with:
-        python-version: 3.8
+        python-version: 3.12
     - name: Set up submodules
       uses: ./.github/actions/deps/submodules
       with: