Fix if statement

Author: dstansby

.github/workflows/ci.yaml

@@ -44,7 +44,7 @@ jobs:
 
       - name: Install clang
         shell: "bash -l {0}"
-        if: ${{ matrix.platform == 'macos-12' }}
+        if: ${{ matrix.platform }} == 'macos-12'
         run: |
           conda activate env
           conda install -y clang<17