ci: add autopep8 check to checks.yml

Add to new autopep8 check to the checks suit. Ideally we would
move the `test.src` test over from tests.yml, but running that
in an updated container leads to a whole lot of new warnings,
most of them related to "unspecified encoding" in `open` calls.

.github/workflows/checks.yml

@@ -57,6 +57,24 @@ jobs:
           ignore_words_list: msdos, pullrequest
           skip: ./.git,coverity,rpmbuild,samples
 
+  source:
+    name: "Source code checks"
+    runs-on: ubuntu-latest
+    steps:
+    - name: "Clone Repository"
+      uses: actions/checkout@v2
+    - name: "Run Tests"
+      uses: osbuild/containers/src/actions/privdocker@e4de123f43b95e99dfe8eed0bd5a1cd58db50715
+      with:
+        image: ghcr.io/osbuild/osbuild-ci:latest-202208041541
+        run: |
+          git config --global --add safe.directory /osb/workdir
+          python3 -m pytest \
+            test/src/test_pylint.py \
+            -k autopep8 \
+            --rootdir=. \
+            -v
+
   mypy:
     name: "Mypy check"
     runs-on: ubuntu-latest