Systems accepting URIs should treat schemes as case-insensitive
([RFC 3986 Section 3.1](https://www.rfc-editor.org/rfc/rfc3986#section-3.1)):
> An implementation should accept uppercase letters as equivalent to
> lowercase in scheme names (e.g., allow "HTTP" as well as "http") for
> the sake of robustness
PiperOrigin-RevId: 528735287
