Fix tox version for CI

Fixes open-telemetry#3079

Author: ocelotl

.github/workflows/test.yml

@@ -46,6 +46,7 @@ jobs:
           python-version: ${{ env[matrix.python-version] }}
           architecture: 'x64'
       - name: Install tox
+        run: pip install tox==3.27.1
         run: pip install -U tox-factor
       - name: Cache tox environment
         # Preserves .tox directory between runs for faster installs