TST,CI: Add workflow to check sdist.

Author: rossbar

.github/workflows/test.yml

@@ -122,3 +122,37 @@ jobs:
         run: |
           make -C doc html SPHINXOPTS="-nT"
           make -C doc latexpdf SPHINXOPTS="-nT"
+
+  test-sdist:
+    runs-on: ${{ matrix.os }}-latest
+    strategy:
+      matrix:
+        os: [ubuntu]
+        python-version: ["3.12", "3.13", "3.14"]
+    steps:
+      - uses: actions/checkout@v5
+
+      - name: Python setup
+        uses: actions/setup-python@v6
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Setup environment
+        run: |
+          python -m pip install --upgrade pip wheel setuptools build
+          python -m pip list
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --group test --group doc
+          pip list
+
+      - name: Install numpydoc from source tarball
+        run: |
+          python -m build
+          python -m pip install --no-binary numpydoc dist/*.tar.gz
+          pip list
+
+      - name: Run test suite
+        run: |
+          pytest -v --pyargs numpydoc