Use existing zarr-python install

Author: dstansby

.github/workflows/ci.yaml

@@ -20,8 +20,8 @@ jobs:
           [ubuntu-latest, ubuntu-22.04-arm, windows-latest, macos-13, macos-14]
         include:
           # Add one test run for zarr 3.0.x
-          - zarr-version: "3.0.*"
-            python-version: "3.11"
+          - python-version: "3.12"
+            zarr-version: "3.0.*"
             platform: "ubuntu-latest"
 
     defaults:
@@ -59,20 +59,19 @@ jobs:
         run: |
           export DISABLE_NUMCODECS_AVX2=""
           python -m pip install -v -e .[test,test_extras,msgpack,crc32c,pcodec,zfpy]
-          python -m pip install zarr==${{ matrix.zarr-version }}
 
       - name: Install zarr-python
         # Since zarr v3 requires numpy >= 1.25, on Python 3.11 leave it out
         # so we can have some tests of our minimum version of numpy (1.24)
         if: matrix.python-version != '3.11'
-        run: python -m pip install zarr>=3
+        run: python -m pip install zarr==${{ matrix.zarr-version }}
 
       - name: List installed packages
         run: python -m pip list
 
       - name: Run tests
         shell: "bash -l {0}"
-        run: pytest -v
+        run: pytest -v numcodecs/tests
 
       - uses: codecov/codecov-action@v5
         with: