Linked MRs links are invalid if they belong to a different project

Problem/Motivation

Linked MRs links are invalid if they belong to a different project.
This also affects the "Sync from related" button, which will fail.

Steps to reproduce

e.g. https://www.drupal.org/api-d7/node/3541006.json?related_mrs=1 →

related_mrs shows

related_mrs: [
"https://git.drupalcode.org/project/canvas/-/merge_requests/19",
"https://git.drupalcode.org/project/canvas/-/merge_requests/1475"
]

but should be

related_mrs: [
"https://git.drupalcode.org/project/canvas/-/merge_requests/19",
"https://git.drupalcode.org/project/experience_builder/-/merge_requests/1475"
]

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes