docs: align vllm source branch with 0.23

[xzh25]

Summary

• update the source-build guide to clone the vLLM release branch that matches current vllm-metax master
• change the example vLLM branch from releases/v0.22.0 to releases/v0.23.0
• add a short note that current master is aligned with vLLM v0.23.0

Validation

• git diff --check
• verified setup.py returns 0.23.0
• verified https://github.com/vllm-project/vllm has refs/heads/releases/v0.23.0

[gemini-code-assist]

Code Review

This pull request updates the MACA installation documentation to recommend cloning the vLLM branch for version v0.23.0 instead of v0.22.0, aligning it with the current vllm-metax version. There are no review comments, so I have no feedback to provide.

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[xzh25]

This docs-only PR is ready for review.

It aligns the MACA source build guide with the current vLLM-metax master version:

• setup.py returns 0.23.0
• vLLM upstream has refs/heads/releases/v0.23.0
• The guide currently still points to releases/v0.22.0

Validation done:

• git diff --check: passed
• version/branch check: passed
• Gemini Code Assist reported no review comments.