[workflows:tests] restore Python 3.5 usage

https://github.com/actions/setup-python/issues/866

.github/workflows/tests.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "pypy3.9"]
+        python-version: ["3.5", "3.6", "3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "pypy3.9"]
 
     steps:
     - uses: actions/checkout@v4
@@ -29,6 +29,8 @@ jobs:
       uses: actions/setup-python@v5
       with:
         python-version: ${{ matrix.python-version }}
+      env:
+        PIP_TRUSTED_HOST: "pypi.python.org pypi.org files.pythonhosted.org"
 
     - name: Install dependencies
       run: |