[ci] [R-package] clang-18 jobs failing: Unable to locate package clang-18

[jameslamb]

Description

CI jobs across multiple PRs have been failing like this for the last few days:

Reading state information...
E: Unable to locate package clang-18
E: Unable to locate package clangd-18
E: Unable to locate package clang-format-18
E: Unable to locate package clang-tidy-18
E: Unable to locate package clang-tools-18
E: Unable to locate package lldb-18
E: Unable to locate package lld-18
E: Unable to locate package llvm-18-dev
E: Unable to locate package llvm-18-tools
E: Unable to locate package libomp-18-dev
E: Unable to locate package libc++-18-dev
E: Couldn't find any package by regex 'libc++-18-dev'
E: Unable to locate package libc++abi-18-dev
E: Couldn't find any package by regex 'libc++abi-18-dev'
E: Unable to locate package libclang-common-18-dev
E: Unable to locate package libclang-18-dev
E: Unable to locate package libclang-cpp18-dev
E: Unable to locate package libunwind-18-dev
Error: Process completed with exit code 100.

Reproducible example

Example build from #6301: https://github.com/microsoft/LightGBM/actions/runs/7795162057/job/21344942028?pr=6301

This is only happening with clang-18 specifically.

Additional Comments

Instructions for installing development versions of LLVM: https://apt.llvm.org/

This failing CI job was added in #6265 about 3 weeks ago, and has been working since then.

[github-actions]

This issue has been automatically locked since there has not been any recent activity since it was closed.
To start a new related discussion, open a new issue at https://github.com/microsoft/LightGBM/issues including a reference to this.