Denominator of publisher-github artifacts spinner is not always accurate

### Pre-flight checklist

- [X] I have read the [contribution documentation](https://github.com/electron-userland/electron-forge/blob/master/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [code of conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project uses.
- [X] I have searched the issue tracker for a bug that matches the one I want to file, without success.

### Electron Forge version

6.0.0-beta.61

### Electron version

v15.3.0

### Operating system

windows-latest (GitHub Actions)

### Last known working Electron Forge version

_No response_

### Expected behavior

The artifacts upload counter should show the total number of artifacts to upload in the denominator, and the artifacts uploaded so far in the numerator.

### Actual behavior

The denominator is always 1 in Windows builds using `@electron-forge/maker-squirrel`:
```
- Uploading Artifacts 0/1 to v0.21.0
✔ Uploading Artifacts 3/1 to v0.21.0
```
I'm not sure what it is about Windows specifically, but I haven't seen this issue on Mac builds with `@electron-forge/maker-dmg` or `@electron-forge/maker-zip`. Maybe it has something to do with the way artifacts are "grouped" by that maker?

### Steps to reproduce

Configure a project using `@electron-forge/maker-squirrel` and build (on Windows).

### Additional information

_No response_