Changing around assignees for PRs causes timeline to hide until refresh

[rzhao271]

Testing #6991

For PR microsoft/vscode-wiki#319, I assigned myself, then unassigned myself and assigned Michael in one go, then assigned myself and unassigned Michael in one go.

I noticed that when changing around the assignees that the PR timeline view would hide right after the change, but that it would display the changes properly after it fully re-rendered. This bug did not seem to occur when I was testing the TPI with a GitHub issue.