MSRV is broken

[jeckersb]

7842a61#diff-fe45e8cd8b566039edc4c6a4e80f355754d32078b45e465a407e22e27c39741aR1246 contains a call to Arc::into_inner which was only stabilized in 1.70. Newest clippy (from 1.78) catches this now whereas it didn't before:

$ cargo clippy -- -D clippy::correctness -D clippy::suspicious
    Checking bootc-lib v0.1.10 (/var/home/jeckersb/git/bootc/lib)
error: current MSRV (Minimum Supported Rust Version) is `1.64.0` but this item is stable since `1.70.0`
    --> lib/src/install.rs:1277:26
     |
1277 |     if let Some(state) = Arc::into_inner(state) {
     |                          ^^^^^^^^^^^^^^^
     |
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#incompatible_msrv
     = note: `-D clippy::incompatible-msrv` implied by `-D clippy::suspicious`
     = help: to override `-D clippy::suspicious` add `#[allow(clippy::incompatible_msrv)]`

error: could not compile `bootc-lib` (lib) due to 1 previous error

Currently we define MSRV as 1.64.0 so we either need to bump that or use an alternative like Arc::try_unwrap.

Probably should add CI to sanity check MSRV as well. Bah as I write this now I see another MSRV issue:

error: package `serde_with_macros v3.8.1` cannot be built because it requires rustc 1.65 or newer, while the currently active rustc version is 1.64.0

[jeckersb]

For reference, cargo msrv gives 1.74.1 as the actual current MSRV. 9.4 has 1.75.0 so bumping to 1.75.0 seems reasonable. And then add CI to make sure we don't accidentally pull something in that requires newer.