ci: fix multus installation

[zhangzujian]

• Make sure you have followed Kube-OVN Code Style.

What type of this PR

• CI

Which issue(s) this PR fixes:

Fixes #(issue-number)

WHAT

🤖 Generated by Copilot at fa7858e

Updated MULTUS_IMAGE in Makefile to use snapshot tag. This is to test kube-ovn with the latest multus-cni version.

🤖 Generated by Copilot at fa7858e

MULTUS_IMAGE changed
To test kube-ovn with snapshot
MULTUS_YAML same

HOW

🤖 Generated by Copilot at fa7858e

• Update multus-cni image to use snapshot tag (link)

[github-actions]

• The commit message should provide more context about the changes made in this patch.
• It is not clear why the MULTUS_IMAGE was changed from stable to snapshot. The commit message should explain this change or add a comment in the code explaining it.
• The format of the Makefile seems consistent, but it would be good to double-check for any potential errors.
• There are no performance issues that can be identified from this diff.
• It might be helpful to add comments in the Makefile to explain what each variable is used for and how it affects the build process.

[oilbeater]

Any issue with the multus stable image?

[zhangzujian]

We are using yaml from the master branch, which has changed the image tag from stable to snapshot.

This patch is supposed to fix the occasional multus installation failure:
https://github.com/kubeovn/kube-ovn/actions/runs/4624461863/jobs/8179433733