Temporarily call brew update to unblock the CI (#524)

Author: alexsavulescu

.github/workflows/coreneuron-ci.yml

@@ -45,6 +45,7 @@ jobs:
       - name: Install homebrew packages
         if: startsWith(matrix.os, 'macOS')
         run: |
+          brew update
           brew install coreutils bison flex boost openmpi
         shell: bash