rustup ought to tell rustls an ALPN

[ctz]

Problem you are trying to solve

Noted in #4305 -- because rustup passes a pre-built rustls configuration into reqwest, it is responsible for configuring the rustls::ClientConfig::alpn_protocols field. This probably has no significant impact given the simple workloads of rustup, but disabling ALPN (and therefore HTTP2) is probably an unintended variance from the curl backend.

Solution you'd like

Set ALPN so HTTP2 can be negotiated.

Notes

No response