Try to get GH CI to run

* Remove added libyaml-dev - it's already installed
* Re pin PyYAML to 3.9 rather than 3.10

.github/workflows/tox.yaml

@@ -19,7 +19,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        sudo apt-get install -q --yes libxml2-dev libxslt1-dev libyaml-dev
+        sudo apt-get install -q --yes libxml2-dev libxslt1-dev
         python -m pip install --upgrade pip
         pip install tox tox-gh-actions
     - name: Lint with tox

requirements.txt

@@ -11,8 +11,8 @@ async_generator
 pyopenssl<22.1.0
 
 boto3<1.25
-PyYAML<=4.2,>=3.0; python_version < '3.10'
-PyYAML>=5.1; python_version >= '3.10'
+PyYAML<=4.2,>=3.0; python_version < '3.9'
+PyYAML>=5.1; python_version >= '3.9'
 flake8>=2.2.4
 flake8-docstrings
 flake8-per-file-ignores