feat: Add GitHub Actions workflow to test distributions on TestPyPI

- Creates .github/workflows/test-pypi-release.yml
- Automatically triggered by: manual dispatch (workflow_dispatch) or tagged releases (v* and test-release-*)
- Build stage: Creates wheel and sdist distributions using hatch
- Upload stage: Publishes distributions to TestPyPI (not production PyPI)
- Test stage: Validates installation from TestPyPI across Python 3.9 and 3.11
- Includes smoke tests to verify basic zarr operations work after installation
- Properly configured with GitHub environment secrets and fail-fast strategy

This workflow catches packaging issues early and validates the release process before pushing to production PyPI.

Fixes zarr-developers#3798

Author: Test User

.github/workflows/test-pypi-release.yml

@@ -1,3 +1,4 @@
+---
 name: Test PyPI Release
 
 on:
@@ -91,7 +92,7 @@ jobs:
           import zarr
           print(f'zarr version: {zarr.__version__}')
           print(f'zarr location: {zarr.__file__}')
-          
+
           # Basic functionality test
           store = zarr.MemoryStore()
           root = zarr.open_group(store=store, mode='w')

changes/3798.feature.md

@@ -0,0 +1 @@
+Add GitHub Actions workflow to test distributions on TestPyPI before releases. This workflow validates the package build process, ensures uploads work correctly, and confirms installation from TestPyPI succeeds across multiple Python versions, catching packaging issues early.