For types such as github, the specification states that name should be lowercased, but not the version.
https://github.com/package-url/purl-spec/blob/master/PURL-TYPES.rst#github

Git tags and branches however can be case sensitive.

Looking at the code the functiontypeAdjustName not only passes the name, but is passing name and version, eg. purl-spec@244fd47e07d1004 and as such the version gets lowercased along with the name.

https://github.com/package-url/packageurl-go/blob/master/packageurl.go#L267