[CI] fix apt_sources error of focal in docker_build

[EmmonsCurse]

Motivation

Fix the Docker build failure caused by using Ubuntu 22.04 (Jammy) apt sources in a Ubuntu 20.04 (Focal) base image, which resulted in package version conflicts.

Remove accuracy_test and stable_test in .github/workflows/ci_image_update.yml

Modifications

Updated /etc/apt/sources.list in the Dockerfile to use Ubuntu 20.04 (Focal) repositories.

Usage or Command

No manual command change required.

Accuracy Tests

No need.

Checklist

• Add at least a tag in the PR title.
  • Tag list: [[FDConfig],[APIServer],[Engine], [Scheduler], [PD Disaggregation], [Executor], [Graph Optimization], [Speculative Decoding], [RL], [Models], [Quantization], [Loader], [OP], [KVCache], [DataProcessor], [BugFix], [Docs], [CI], [Optimization], [Feature], [Benchmark], [Others], [XPU], [HPU], [GCU], [DCU], [Iluvatar], [Metax]]
  • You can add new tags based on the PR content, but the semantics must be clear.
• Format your code, run pre-commit before commit.
• Add unit tests. Please write the reason in this PR if no unit tests.
• Provide accuracy results.
• If the current PR is submitting to the release branch, make sure the PR has been submitted to the develop branch, then cherry-pick it to the release branch with the [Cherry-Pick] PR tag.

[paddle-bot]

Thanks for your contribution!