update docker list for pypy

Author: altendky

.github/workflows/ci.yml

@@ -31,6 +31,8 @@ jobs:
               3.6: docker://python:3.6-buster
               3.7: docker://python:3.7-buster
               3.8: docker://python:3.8-buster
+              pypy2: docker://pypy:2-stretch
+              pypy2: docker://pypy:3-stretch
           - name: Windows
             runs-on: windows-latest
             python_platform: win32
@@ -61,9 +63,11 @@ jobs:
           - name: PyPy 2
             tox: pypy2
             action: pypy2
+            docker: pypy2
           - name: PyPy 3
             tox: pypy3
             action: pypy3
+            docker: pypy3
         reactor:
           - name: default
             tox: default