Long commit messages break display of commit message tooltip

Summary

Whenever the commit message is too long, hovering the commit hash in a pull request breaks the display of commit message tooltip.

Environment

• Replicated in Google Chrome and Mozilla Firefox

Steps to Reproduce

1. Create a commit whose message is at least 117 characters long.
2. Create a pull request that includes this commit.
3. Go to that pull request - "diff" section, select that commit using "Show diff of".
4. Hover the hash of that commit to see the commit message tooltip.

Actual Results

The commit message tooltip is displayed offset / misaligned to the left:

Expected Results

The commit message tooltip should be displayed like this (from 5.5.x):

Workaround

There are no known workarounds thus far.