Stop setting the default source branch to 'main'

[grahamc]

Description

This will cause new pulls from i.d.s to fetch the latest tag.

Checklist

• Tested changes against a test repository
• Added or updated relevant documentation (leave unchecked if not applicable)
• (If this PR is for a release) Updated README to point to the new tag (leave unchecked if not applicable)

[colemickens]

Presumably this falls through to return${urlPrefix}/latest/${binarySuffix};? Just making sure, that still looks unversioned.

[grahamc]

Presumably this falls through to return${urlPrefix}/latest/${binarySuffix};? Just making sure, that still looks unversioned.

That's right, it'll continue pulling an unversioned "Latest". Ideally we could pull these artifacts from flakehub with nice semver goodness.