feat: Add GitHub Actions workflow to test distributions on TestPyPI (fixes #3798)

.github/workflows/testpypi.yml

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+name: Publish distributions to TestPyPI
+
+on:
+  workflow_dispatch:
+  push:
+    tags:
+      - "v*-testpypi"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.12"
+
+      - name: Install build tools
+        run: python -m pip install --upgrade build twine
+
+      - name: Build distributions
+        run: python -m build
+
+      - name: Check distributions
+        run: twine check dist/*
+
+      - name: Upload artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: testpypi-dist
+          path: dist/
+          retention-days: 1
+
+  publish-testpypi:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: testpypi
+      url: https://test.pypi.org/p/zarr
+    permissions:
+      id-token: write
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: testpypi-dist
+          path: dist
+
+      - name: Publish to TestPyPI
+        uses: pypa/gh-action-pypi-publish@v1.13.0
+        with:
+          repository-url: https://test.pypi.org/legacy/
+
+  test-install:
+    needs: publish-testpypi
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.11", "3.12", "3.13"]
+    steps:
+      - uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+
+      - name: Wait for TestPyPI package
+        run: sleep 30
+
+      - name: Install from TestPyPI
+        run: |
+          pip install --index-url https://test.pypi.org/simple/ \
+            --extra-index-url https://pypi.org/simple/ \
+            zarr
+
+      - name: Test import
+        run: python -c "import zarr; print(zarr.__version__)"

changes/3798.feature.md

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+Add GitHub Actions workflow to test distributions on TestPyPI before release