Ring no longer builds with Rust 1.61 due to cc dependency

[uweigand]

As of cc 1.0.95, the minimum required Rust version is 1.63: rust-lang/cc-rs#1031

However, the Ring CI still attempts to build with 1.61, which now fails with:

error: package `cc v1.0.95` cannot be built because it requires rustc 1.63 or newer, while the currently active rustc version is 1.61.0

We should either increase the minimum required Rust level for Ring as well, or else force use of an older cc version.

[briansmith]

We should either increase the minimum required Rust level for Ring as well, or else force use of an older cc version.

The user of ring could already force an older cc-rs version if they want to, using their Cargo.lock. However, I updated the MSRV of ring to 1.63 in PR #2037 so that I don't have to add any complication to the GitHub Actions configuration regarding this.