Upgrade reqwest to 0.12

[zecakeh]

This new version just came out and uses the new major version 1.x of the http crate.

Dependencies still depending on older versions of reqwest/http:

• mas-oidc-client (for the experimental-oidc feature): Upgrade hyper/http to version 1.x matrix-authentication-service#2530
• ruma: Upgrade http to version 1.x ruma/ruma#1748

[zecakeh]

This was done in #3362. Should we keep this open to remember to track the status of http in matrix-authentication-service?

[bnjbvr]

We can close this one, and get back to the matrix-authentication-service one later; I suspect that as soon as they've bumped the http crate, we'll eventually get a (failing) PR from dependabot.

Thanks for your work here Kevin!