CI needs Python 3.9 due to a nonstandard construct

Author: jepler

.github/workflows/build.yml

@@ -22,10 +22,12 @@ jobs:
         awk -F '\/' '{ print tolower($2) }' |
         tr '_' '-'
         )
-    - name: Set up Python 3.x
+    # Python 3.10 rejects a nonstandard Python syntax that is required by
+    # CircuitPython's asyncio implementation
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: "3.x"
+        python-version: "3.9"
     - name: Versions
       run: |
         python3 --version

.github/workflows/release.yml

@@ -24,10 +24,12 @@ jobs:
         awk -F '\/' '{ print tolower($2) }' |
         tr '_' '-'
         )
-    - name: Set up Python 3.x
+    # Python 3.10 rejects a nonstandard Python syntax that is required by
+    # CircuitPython's asyncio implementation
+    - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
-        python-version: "3.x"
+        python-version: "3.9"
     - name: Versions
       run: |
         python3 --version
@@ -69,7 +71,7 @@ jobs:
       if: contains(steps.need-pypi.outputs.pyproject-toml, 'pyproject.toml')
       uses: actions/setup-python@v2
       with:
-        python-version: '3.x'
+        python-version: '3.9'
     - name: Install dependencies
       if: contains(steps.need-pypi.outputs.pyproject-toml, 'pyproject.toml')
       run: |