templates: use github default branch instead of hardcoded main

[gucio321]

Description

Hi,
I used to call my default git branch master so I've created my custom quarto template like this and have noticed that it doesn't work.
It turned out that I had to add @master to make it work.
Adding the main branch helped as well.

Because git tracks repository default branch, there is no need in my opinion to hardcode main as the default branch.

[mcanouil]

When no @ref is given, githubLatestUrlProvider in src/extension/extension-host.ts always downloads archive/refs/heads/main. It never asks GitHub for the repository's default branch. On a repository whose default branch is master, that request returns 404 and quarto use template stops with Extension not found in local or remote sources. This is tracked in #14821, which reports the same defect for quarto add.

A small note on "git tracks the repository default branch": git itself has no such setting. A remote repository has a HEAD that points at one branch, and git clone follows it. GitHub's "default branch" is that pointer. Quarto doesn't use git here, though. It downloads an archive over HTTP from a URL with main written into it, so the remote HEAD never comes into play.

In the meantime, you can:

• Add the branch explicitly: quarto use template owner/repo@master.
• Use the Quarto Wizard extension for VS Code and Positron. Its "Use Template" command finds the default branch from the extension registry or from the GitHub API before it downloads, so master repositories work without @master.

Closing as duplicate in favour of:

• quarto add/use owner/repo fails on repos whose default branch isn't main #14821