build: relax typeguard constraints following TensorFlow release (#440)

* relax version constraint on typeguard as latest TensorFlow release no longer causes dependency clash
* upgrade typing-extensions version in Python 3.8 CI to circumvent dependency clash

.github/workflows/CI.yml

@@ -55,6 +55,8 @@ jobs:
     - name: Test with pytest, generate coverage report (skipping typeguard)
       if: matrix.python-version == '3.8'
       run: |
+        # https://github.com/scikit-hep/cabinetry/issues/428
+        pip install --upgrade typing_extensions
         # skip typeguard for coverage https://github.com/agronholm/typeguard/issues/356
         pytest --runslow --cov-report=xml --typeguard-packages=""
     - name: Test with pytest

setup.py

@@ -16,7 +16,7 @@
             "mypy",
             "types-tabulate",
             "types-PyYAML",
-            "typeguard>=4.0.0,!=4.0.1,!=4.1.*",  # cabinetry#391, cabinetry#428
+            "typeguard>=4.0.0",  # cabinetry#391
             "black",
         ]
     )