[C++] C++ Extra Meson build fails due to missing libxml2 for azure

### Describe the bug, including details regarding any error messages, version, and platform. Since the 22nd of July the C++ Extra Meson build has been failing with: ``` | -- AZ_LIBRARY_VERSION | Vcpkg integrate step. | Vcpkg integrate step - DONE. | CMake Error at /opt/conda/envs/arrow/share/cmake-4.4/Modules/FindPackageHandleStandardArgs.cmake:290 (message): | Could NOT find LibXml2 (missing: LIBXML2_LIBRARY LIBXML2_INCLUDE_DIR) | Call Stack (most recent call first): | /opt/conda/envs/arrow/share/cmake-4.4/Modules/FindPackageHandleStandardArgs.cmake:654 (_FPHSA_FAILURE_MESSAGE) | /opt/conda/envs/arrow/share/cmake-4.4/Modules/FindLibXml2.cmake:181 (find_package_handle_standard_args) | sdk/storage/azure-storage-common/CMakeLists.txt:102 (find_package) | -- Configuring incomplete, errors occurred! azure| CMake configuration: FAILED ../../arrow/cpp/src/arrow/meson.build:399:31: ERROR: Failed to configure the CMake subproject: Could NOT find LibXml2 (missing: LIBXML2_LIBRARY LIBXML2_INCLUDE_DIR) A full log can be found at /build/cpp/meson-logs/meson-log.txt ``` Link to the first failure: - https://github.com/apache/arrow/actions/runs/29880688862/job/88800704317 ### Component(s) C++