Add unit tests to CI (#407)

* Add unit tests to CI

The unit tests were not being run during CI. This adds a GitHub Action
for it.

* Add changelog fragment

.github/workflows/ci.yml

@@ -112,6 +112,29 @@ jobs:
         run: make test-molecule
         working-directory: ./ansible_collections/community/kubernetes
 
+  unit:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python_version: ['2.7', '3.7']
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v2
+        with:
+          path: ansible_collections/community/kubernetes
+
+      - name: Set up Python ${{ matrix.python_version }}
+        uses: actions/setup-python@v1
+        with:
+          python-version: ${{ matrix.python_version }}
+
+      - name: Install ansible base (devel branch)
+        run: pip install https://github.com/ansible/ansible/archive/devel.tar.gz --disable-pip-version-check
+
+      - name: Run unit tests on Python ${{ matrix.python_version }}
+        run: make test-unit PYTHON_VERSION=${{ matrix.python_version }}
+        working-directory: ./ansible_collections/community/kubernetes
+
   downstream-sanity-29:
     runs-on: ubuntu-latest
     strategy: