[ci] fix installation of clang-18 (fixes #6306)

[jameslamb]

Fixes #6306

These modifications are based on the "Debian" section at https://apt.llvm.org/.

[shiyu1994]

It seems that the Mariner Linux agent fails to start again in this CI. Let's check if this happens more frequently than before and to decide whether to take some actions.

[jameslamb]

It seems that the Mariner Linux agent fails to start again in this CI.

Thanks for pointing that out @shiyu1994 , yes I agree. Over the last few weeks, I think I've had to restart at least one Azure DevOps job on almost every commit. I'll try to capture more logs the next time I see that, maybe we can find the root cause.

[jameslamb]

thanks for the quick response everyone!

[jameslamb]

I just saw a few more of these: https://dev.azure.com/lightgbm-ci/lightgbm-ci/_build/results?buildId=15757&view=results

Starting: Initialize job
Agent name: 'lgbub6c5400017H'
Agent machine name: 'lgbub6c5400017H'
Current agent version: '3.232.3'
Agent running as: 'AzDevOps'
Prepare build directory.
Set build variables.
Download all required tasks.
Downloading task: 1ESHostedPoolValidation (1.0.26350327)
Downloading task: CmdLine (2.231.1)
Downloading task: Bash (3.231.5)
Downloading task: PublishBuildArtifacts (1.231.1)
Downloading task: ComponentGovernanceComponentDetection (0.2420208.1)
Checking job knob settings.
   Knob: DockerActionRetries = true Source: $(VSTSAGENT_DOCKER_ACTION_RETRIES) 
   Knob: AgentEnablePipelineArtifactLargeChunkSize = true Source: $(AGENT_ENABLE_PIPELINEARTIFACT_LARGE_CHUNK_SIZE) 
   Knob: ContinueAfterCancelProcessTreeKillAttempt = true Source: $(VSTSAGENT_CONTINUE_AFTER_CANCEL_PROCESSTREEKILL_ATTEMPT) 
   Knob: ProcessHandlerTelemetry = true Source: $(AZP_75787_ENABLE_COLLECT) 
   Knob: IgnoreVSTSTaskLib = true Source: $(AZP_AGENT_IGNORE_VSTSTASKLIB) 
   Knob: FailJobWhenAgentDies = true Source: $(FAIL_JOB_WHEN_AGENT_DIES) 
   Knob: CheckForTaskDeprecation = true Source: $(AZP_AGENT_CHECK_FOR_TASK_DEPRECATION) 
   Knob: MountWorkspace = false Source: $(AZP_AGENT_MOUNT_WORKSPACE) 
Finished checking job knob settings.
##[error]File not found: 'docker'

[jameslamb]

opened #6316 so we can discuss the CI instability there