Show warning on modelling page when personal git access token is invalid

[dwl285]

Steps to reproduce:

1. Connect a project to github
2. Add a valid personal access token
3. Create a branch
4. Remove the personal access token
5. Re-open the branch that was just created and make some file changes

Expected result: A warning shown next to the branch selector: "Your personal git access token is invalid. Please add a valid access token before making any changes to your project"

Actual result: There is no message shown next to the branch selector

[jefffriesen]

I was having this ticket's problem (referenced in slack). Now I have a similar issue. I hope it is related enough to add context to this ticket and not noise.

Here's what happened. I had to rename the repo that was backing the Dataform project. That is unusual so I realize this is an edge case. I unlinked the Dataform project from the Github repo. I created a new repo with no commits. Then I linked Dataform to that new repo. Dataform pushed master commits properly but not the branch I was working on. The branch I was working on was still in Dataform and working properly but there was no way to commit changes. The button to the right of the branch name didn't show up even after making changes to files nor by creating new files. You can see this in the screenshot (that's a brand new file). I have tried

1. Generating a new Github token and adding it to the Dataform project
2. Hard refresh without cache (command-shift-r)

Neither of these worked. What did work was creating a new branch and pushing it to GitHub. I can confirm on the Github side. So this isn't a blocker for me - I can create a new branch and copy and paste work from my other branch into the new branch and push that. But it did take me a while futzing around trying understand the problem. Attached is a screenshot of the branch that I want to push but doesn't have the commit button.

I hope this helps narrow down the problem. Thanks