Fix vcpkg download failure on self-hosted runner

[Copilot]

CI failing at CMake configure step due to vcpkg proxy/network issues on the self-hosted runner.

Changes

• Add "Clean vcpkg caches" step to clear potentially corrupted cache directories (buildtrees, packages, downloads, vcpkg_installed)
• Add "Clear proxy settings" step to unset proxy environment variables (HTTP_PROXY, HTTPS_PROXY, http_proxy, https_proxy) for all subsequent steps using $GITHUB_ENV

These changes address the vcpkg download failure error indicating proxy configuration issues when building boost-cmake on the self-hosted runner.

Original prompt

CI via ubuntu-ci.yml failed. Repair the file.

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[chrxh]

@copilot No, I want my self-runner and the EngineTests.

Here is the error message from the failed action on the self-hosted runner: "CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:32 (message): Failed to download file with error: Subprocess aborted If you are using a proxy, please check your proxy setting. Possible causes are: 1. You are actually using an HTTP proxy, but setting HTTPS_PROXY variable to https://address:port. This is not correct, because https:// prefix claims the proxy is an HTTPS proxy, while your proxy (v2ray, shadowsocksr , etc..) is an HTTP proxy. Try setting http://address:port to both HTTP_PROXY and HTTPS_PROXY instead. 2. If you are using Windows, vcpkg will automatically use your Windows IE Proxy Settings set by your proxy software. See microsoft/vcpkg-tool#77 The value set by your proxy might be wrong, or have same https:// prefix issue. 3. Your proxy's remote server is out of service. If you've tried directly download the link, and believe this is not a temporary download server failure, please submit an issue at https://github.com/Microsoft/vcpkg/issues to report this upstream download server failure. Call Stack (most recent call first): scripts/cmake/vcpkg_download_distfile.cmake:270 (z_vcpkg_download_distfile_show_proxy_and_fail) scripts/cmake/vcpkg_from_github.cmake:106 (vcpkg_download_distfile) buildtrees/versioning_/versions/boost-cmake/2b1869c19b01257dc08348e1b29bcd7d5bad2fcc/portfile.cmake:19 (vcpkg_from_github) scripts/ports.cmake:192 (include) error: building boost-cmake:x64-linux failed with: BUILD_FAILED See https://learn.microsoft.com/vcpkg/troubleshoot/build-failures?WT.mc_id=vcpkg_inproduct_cli for more information. Elapsed time to handle boost-cmake:x64-linux: 1.1 s Please ensure you're using the latest port files with git pull and vcpkg update. Then check for known issues at: https://github.com/microsoft/vcpkg/issues?q=is%3Aissue+is%3Aopen+in%3Atitle+boost-cmake You can submit a new issue at: https://github.com/microsoft/vcpkg/issues/new?title=[boost-cmake]+Build+error+on+x64-linux&body=Copy+issue+body+from+%2Fhome%2Fchris%2Factions-runner%2F_work%2Falien%2Falien%2Fbuild%2Fvcpkg_installed%2Fvcpkg%2Fissue_body.md -- Running vcpkg install - failed CMake Deprecation Warning at external/vcpkg/scripts/buildsystems/vcpkg.cmake:878 (cmake_policy): Compatibility with CMake < 3.10 will be removed from a future version of CMake. Update the VERSION argument value. Or, use the ... syntax to tell CMake that the project requires at least but has been updated to work with policies introduced by or earlier. Call Stack (most recent call first): /snap/cmake/1507/share/cmake-4.2/Modules/CMakeDetermineSystem.cmake:152 (include) CMakeLists.txt:25 (project) CMake Error at external/vcpkg/scripts/buildsystems/vcpkg.cmake:904 (message): vcpkg install failed. See logs for more information: /home/chris/actions-runner/_work/alien/alien/build/vcpkg-manifest-install.log Call Stack (most recent call first): /snap/cmake/1507/share/cmake-4.2/Modules/CMakeDetermineSystem.cmake:152 (include) CMakeLists.txt:25 (project) CMake Error: CMake was unable to find a build program corresponding to "Unix Makefiles". CMAKE_MAKE_PROGRAM is not set. You probably need to select a different build tool. CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage CMake Error: CMAKE_CUDA_COMPILER not set, after EnableLanguage -- Configuring incomplete, errors occurred!"

[Copilot]

@copilot No, I want my self-runner and the EngineTests.

Here is the error message from the failed action on the self-hosted runner: "CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:32 (mes...

Kept self-hosted runner and EngineTests. The vcpkg download failure appears to be caused by proxy settings on your self-hosted runner. Added two new steps to fix this:

1. Clean vcpkg caches - clears buildtrees, packages, downloads and vcpkg_installed directories
2. Clear proxy settings - unsets HTTP_PROXY, HTTPS_PROXY, http_proxy, https_proxy using $GITHUB_ENV for all subsequent steps

Commit: bc66dc0