ci: always ensure the latest brew version in installed

Hopefully fixes the following error happening in the macOS Ci
intermittently:
```
-- Found Boost: /usr/local/lib/cmake/Boost-1.83.0/BoostConfig.cmake (found version "1.83.0") found components: filesystem program_options regex system json nowide
-- Found Python3: /usr/local/Frameworks/Python.framework/Versions/3.12/bin/python3.12 (found version "3.12.0") found components: Development Interpreter Development.Module Development.Embed
CMake Error at /usr/local/lib/cmake/Boost-1.83.0/BoostConfig.cmake:141 (find_package):
  Found package configuration file:
-- Configuring incomplete, errors occurred!

    /usr/local/lib/cmake/boost_python-1.83.0/boost_python-config.cmake

  but it set boost_python_FOUND to FALSE so package "boost_python" is
  considered to be NOT FOUND.  Reason given by package:

  No suitable build variant has been found.

  The following variants have been tried and rejected:

  * libboost_python311-mt.dylib (3.11, Boost_PYTHON_VERSION=3.12)

  * libboost_python311-mt.a (3.11, Boost_PYTHON_VERSION=3.12)

  * libboost_python311.dylib (3.11, Boost_PYTHON_VERSION=3.12)

  * libboost_python311.a (3.11, Boost_PYTHON_VERSION=3.12)

Call Stack (most recent call first):
  /usr/local/lib/cmake/Boost-1.83.0/BoostConfig.cmake:262 (boost_find_component)
  /usr/local/Cellar/cmake/3.27.7/share/cmake/Modules/FindBoost.cmake:594 (find_package)
  src/CMakeLists.txt:104 (find_package)
  src/CMakeLists.txt:137 (build_pycsdiff)
```

Author: lzaoral

.github/workflows/macos.yml

@@ -27,7 +27,7 @@ jobs:
 
       - name: Install dependencies
         run: |
-          brew upgrade
+          brew update
           brew install boost boost-python3 help2man
 
       - name: Build and check