fix: numcodecs build in downstream

Author: maxrjones

.github/workflows/downstream.yml

@@ -85,7 +85,8 @@ jobs:
       - name: Install numcodecs with test-zarr-main group
         working-directory: numcodecs
         run: |
-          uv sync --group dev --group test-zarr-main
+          uv pip install meson-python
+          uv sync --group dev --group test-zarr-main --no-build-isolation
           uv pip install --no-build-isolation -e .
 
       - name: Override zarr-python with branch version