ci: Add workaround for vcpkg's libevent package

This change is necessary for Windows GHA images, which provide
CMake >= 4.0.

Author: hebasto

.github/workflows/ci.yml

@@ -205,6 +205,8 @@ jobs:
         run: |
           echo "set(VCPKG_BUILD_TYPE release)" >> "${VCPKG_INSTALLATION_ROOT}/triplets/x64-windows.cmake"
           echo "set(VCPKG_BUILD_TYPE release)" >> "${VCPKG_INSTALLATION_ROOT}/triplets/x64-windows-static.cmake"
+          # Workaround for libevent, which requires CMake 3.1 but is incompatible with CMake >= 4.0.
+          sed -i '1s/^/set(ENV{CMAKE_POLICY_VERSION_MINIMUM} 3.5)\n/' "${VCPKG_INSTALLATION_ROOT}/scripts/ports.cmake"
 
       - name: vcpkg tools cache
         uses: actions/cache@v4