[Bug]: secondary branches are not getting deployed for previews.

### Problem description

I had a repository linked to a project that always worked as expected.
I started doing some things with paths in Deno and therefore I decided to change a folder name from "Server" to "server" since I think it's causing some problems in my code.
When I did that deploy failed because server entry was linked at Server/main.jsx instead of server/main.jsx.
I couldn't find a way to change this path so I unlinked my repository to link it again.
I put everything as I remember it was, pretty basic npm install, npm run build and server/main.jsx as entry point.
I immediately noticed some errors that for some reasons were not present before. I inspect everything and it seems like I simplified my main branch recently and it didn't need a build anymore (so no more package.json etc..).
Not sure why that was working before but let's go on:
I commit a package.json try again and got everything to work.
But...

I lost the possibility to preview secondary branches updates! Before it was automatic, push on a secondary branch and see a deployment on Github with a specific preview link for that branch/commit.

Now it does deployment only when I push on branch.

Also I'm wondering has this changed to Github actions recently? Because I cannot see any old deploy.yml in my old commits, I wonder how it was working before and what are the advantages of this new setup (failing build if one command fails?)

### Steps to reproduce

I tried to replicate like this but I didn't have the same problems:
1. Create a [new repo](https://github.com/andreafuturi/dentist)
2. Link it to Deno Deploy new project and try secondary branch preview deploy

till here everything's fine

3. In the repo edit entry point folder's case from Server/main.jsx to server/main.jsx
4. In Deno Deploy dashboard unlink repo and relink it updating entry point to the new lowercase one.
5. Edit secondary branch and see if preview deployment is launched

In this case everything worked as expected and the preview deployment was launched..
I also don't see any yml file in my repo workflow (like I always did before today)

### Expected behavior

When I push into a secondary branch I expect to see a preview deployment on Github

### Environment

- Deno 2

### Possible solution

If something has changed maybe warn old users before letting them unlink their repo and go into this new system?
But still why removing such a nice feature like secondary branches previews?

### Additional context

Fail of deployment before unlinking of repo

Fail of deployment after unlinking of repo