Fix displaying errors in GitHub pane.

[grokys]

#1787 refactored InfoPanel but didn't update GitHubPaneView with its new behavior. So:

• Don't initially set infoPanel.Visibility to Collapsed: InfoPanel will handle this itself
• Set ShowCloseButton to show the x button to close the error

Fixes #2172
Related #2058

[jcansdale]

If I try to create a PR in a repo that I don't have permissions to push, I see the following.

This is a fix for #2172, but the message is a little obtuse for this to fix completely #2058. I'll update the issue and merge. 👍