I wanted to apply a check in policy in VSTS Git in which whenever a new check in is happening there should be check in policy in which work item linkage is mandatory.
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For git, you can use branch police to check for linked work items.
Instead of pushing change to the target branch directly, you can checkout a source branch from the target branch. Make changes on the source branch. When you create a PR to merge the changes from source branch into target branch, the pull request will check the linked work items before merging.