Allow pypy 3.8/7.3.10 to fail pytest/coverage

There's an issue with coverage and pypy `3.8.15[pypy-7.3.10-final]`, see links for details:
- nedbat/coveragepy#1515
- https://foss.heptapod.net/pypy/pypy/-/issues/3876

.github/workflows/tests.yaml

@@ -8,9 +8,14 @@ jobs:
   tests:
     name: Run all tests
     runs-on: ubuntu-latest
+    continue-on-error: ${{ matrix.continue_on_error }}
     strategy:
       matrix:
-        python_version: ["3.7", "3.8", "3.9", "3.10", "3.11", "pypy-3.7", "pypy-3.8", "pypy-3.9"]
+        python_version: ["3.7", "3.8", "3.9", "3.10", "3.11", "pypy-3.7", "pypy-3.9"]
+        continue_on_error: [false]
+        include:
+          - python_version: "pypy-3.8"]
+            continue_on_error: true
     steps:
       - name: Checkout code
         uses: actions/checkout@v3