GitHub Actions: Update Homebrew utfcpp to 4.0.2 (#1171)

Revert "Fix build on Mac with Homebrew utf8cpp"
This reverts commit 70b4ce79fb.

Is now fixed upstream
https://github.com/nemtrif/utfcpp/pull/113
https://github.com/nemtrif/utfcpp/releases/tag/v4.0.2
https://github.com/Homebrew/homebrew-core/pull/153333

.github/workflows/build.yml

@@ -23,7 +23,9 @@ jobs:
       if: matrix.os == 'ubuntu-latest'
 
     - name: Set up macOS
-      run: brew install cppunit utf8cpp
+      run: |
+        brew update
+        brew install cppunit utf8cpp
       if: matrix.os == 'macos-latest'
 
     - name: Set up Windows