CI/CD updates

- bump checkout to v4
- enable HOMEBREW_NO_INSTALL_UPGRADE to skip upgrading existing
packages (this often fails on attempts to overwrite conflicting
files)

.github/workflows/build.yml

@@ -14,9 +14,10 @@ jobs:
     runs-on: ${{ matrix.os }}
     env:
       HOMEBREW_NO_INSTALLED_DEPENDENTS_CHECK: 1
+      HOMEBREW_NO_INSTALL_UPGRADE: 1
     steps:
     - name: Checkout repository
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
 
     - name: Install packaged dependencies
       run: |