pipeline/python3.8: upgrade astroid to fix KeyError

> File ".../python3.8/site-packages/astroid/__init__.py", line 91, in _inference_tip_cached
>   return iter(_cache[func, node])
> KeyError: (<function infer_named_tuple at 0x7f7e0c3fd9d0>, <Call l.1224 at 0x7f7e0af37ca0>)
https://travis-ci.org/fphammerle/free-disk/jobs/630911474

.github/workflows/python.yml

@@ -22,6 +22,9 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - run: pip install --upgrade pipenv>=2018.10.9
     - run: pipenv sync --dev
+    - run: if python3 -c 'import sys; sys.exit(sys.version_info < (3, 8))'; then
+           pipenv install 'astroid>=2.3.0';
+           fi
     - run: pipenv graph
     - run: pipenv run pylint free_disk
     - run: pipenv run pytest

.travis.yml

@@ -16,6 +16,9 @@ dist: xenial
 install:
 - pip install --upgrade pipenv>=2018.10.9
 - pipenv sync --dev
+- if python3 -c 'import sys; sys.exit(sys.version_info < (3, 8))'; then
+  pipenv install 'astroid>=2.3.0';
+  fi
 - pipenv graph
 
 script: