CI: Re-add Py2.7 test support by using the pre-installed system Python 2.7.

Author: scoder

.github/workflows/ci.yml

@@ -55,9 +55,21 @@ jobs:
 
     - name: Set up Python
       uses: actions/setup-python@v4
+      if: startsWith(matrix.python-version, '3.')
       with:
         python-version: ${{ matrix.python_version }}
 
+    - name: Set up Python2 (Linux)
+      if: matrix.python-version == '2.7' && startsWith(matrix.os, 'ubuntu')
+      run: |
+          sudo ln -fs python2 /usr/bin/python
+          sudo apt-get update
+          sudo apt-get install python-setuptools python2-dev
+          curl https://bootstrap.pypa.io/pip/2.7/get-pip.py --output get-pip.py
+          sudo python2 get-pip.py
+          ls -l /usr/bin/pip* /usr/local/bin/pip*
+          which pip
+
     - name: Install Dependency
       run: |
         python -m pip install -U pip setuptools && python -m pip install -r requirements.txt