upstream: Prevent 500 if no project members have been provided (goharbor/harbor#23642)

[github-actions]

Summary

Cherry-picks upstream Harbor commit 6e827641a from goharbor/harbor#23642.

Upstream Context

• Upstream PR: Prevent 500 if no project members have been provided goharbor/harbor#23642
• Upstream commit: 6e827641a61079b29311cd1c06ef465fdf650534
• Upstream title: Prevent 500 if no project members have been provided
• Upstream author: @Yanni8
• Upstream merged by: @wy65701436
• Upstream approved by: @stonezdj, @wy65701436
• Upstream PR URL: Prevent 500 if no project members have been provided goharbor/harbor#23642
• Upstream commit URL: goharbor/harbor@6e82764

Cherry-Pick Status

• Status: clean
• Base branch: main
• Workflow run: https://github.com/container-registry/harbor-next/actions/runs/31076123559

Upstream Description

Fail softly with a 400 error and an appropriate error message if no members are provided in the POST /api/v2.0/projects/{id}/members request.

Comprehensive Summary of your change

Issue being fixed

Fixes #23639

Please indicate you've done the following:

• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

Review Notes

• Generated by the upstream cherry-pick workflow.
• One upstream commit maps to one Harbor Next PR.
• If this PR is closed without merge, the workflow will not recreate it.

Upstream-Commit: 6e827641a61079b29311cd1c06ef465fdf650534
Upstream-PR: goharbor/harbor#23642
Cherry-Pick-Status: clean