Add an sdist install job

This should hopefully catch issues like,
https://github.com/goodboy/tractor/issues/293

.github/workflows/ci.yml

@@ -28,6 +28,26 @@ jobs:
       - name: Run MyPy check
         run: mypy tractor/ --ignore-missing-imports
 
+  sdist-linux:
+    name: 'sdist'
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Setup python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
+      - name: Build sdist
+        run: python setup.py sdist --formats=zip
+
+      - name: Install sdist from .zips
+        run: python -m pip install dist/*.zip
+
+
   testing-linux:
     name: '${{ matrix.os }} Python ${{ matrix.python }} - ${{ matrix.spawn_backend }}'
     timeout-minutes: 10