[CI] clean up docker image in ci

[jikunshang]

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

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Purpose

clean up docker image in ci, avoid disk full.

Test Plan

Test Result

(Optional) Documentation Update

BEFORE SUBMITTING, PLEASE READ https://docs.vllm.ai/en/latest/contributing (anything written below this line will be removed by GitHub Actions)

[Copilot]

Pull request overview

This PR adds Docker cleanup commands to the CI workflow to prevent disk space exhaustion. The changes ensure that Docker images and unused resources are removed after test runs complete.

• Adds explicit Docker image removal commands for the test container
• Includes Docker system prune to clean up dangling resources

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[Copilot]

Remove the trailing semicolons on these lines. In shell scripts, semicolons are statement terminators and are unnecessary at the end of a line. The other commands in this workflow (e.g., line 40 and 74) do not use trailing semicolons, making these inconsistent with the existing style.

Suggested change

	docker system prune -f || true;
	docker system prune -f || true

[Copilot]

Remove the trailing semicolons on these lines. In shell scripts, semicolons are statement terminators and are unnecessary at the end of a line. The other commands in this workflow (e.g., line 40 and 74) do not use trailing semicolons, making these inconsistent with the existing style.

Suggested change

	docker system prune -f || true;
	docker system prune -f || true