External services UI shows GitHub Enterprise improperly

Created by: sqs

On v3.12.6

Repro:

1. Go to Site admin > Manage repositories > + Add repositories
2. Select GitHub Enterprise (expected: the name field is filled with "GitHub Enterprise", actual: "GitHub")
3. Create it
4. Go back and edit it (expected: the header shows "GitHub Enterprise", actual: "GitHub.com" as in the screenshot below)

I don't know if this is causing any underlying problems or if it's just a visual glitch.

Adding to 3.13 milestone because it is a bug with high potential for confusion or worry. @tsenart Can you please assign/schedule this?