Pin conda used in testing

Author: dstansby

.github/workflows/ci.yaml

@@ -31,7 +31,7 @@ jobs:
         uses: conda-incubator/[email protected]
         with:
           channels: conda-forge
-          miniforge-version: latest
+          miniforge-version: "24.9.2-0"
           python-version: ${{ matrix.python-version }}
 
       - name: Install compilers