proj: MSRV 1.71 -> 1.73

1.71 and 1.72 both hit an ICE building with a static reference to
Rustls' aws-lc-rs HPKE suites. Upstream (sensibly) isn't interested in
fixing bugs in old compilers. We also don't want to bump the upstream
Rustls MSRV for niche errors, or add excessive workarounds. So: let's do
the easy thing and increase rustls-ffi's MSRV to 1.73. The rustls-ffi
project has few downstream consumers at this point and so is more agile
for MSRV bumps than the core crate.

Along the way, match the formatter to the MSRV. It had fallen behind.

.github/workflows/test.yaml

@@ -25,7 +25,7 @@ jobs:
           - nightly
           # MSRV - keep in sync with what rustls and rustls-platform-verifier
           # consider MSRV
-          - 1.71.0
+          - "1.73"
         os: [ ubuntu-latest ]
         # but only stable, clang, and aws-lc-rs on macos (slower platform)
         include:
@@ -256,7 +256,7 @@ jobs:
       - name: Install rust toolchain
         uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: 1.67.1
+          toolchain: "1.73" # Matching MSRV
           components: rustfmt
       - name: Check Rust formatting
         run: cargo fmt --all -- --check

README.md

@@ -21,7 +21,7 @@ to provide the cryptographic primitives.
 
 # Build
 
-You'll need to [install the Rust toolchain](https://rustup.rs/) (version 1.71
+You'll need to [install the Rust toolchain](https://rustup.rs/) (version 1.73
 or above) and a C compiler (`gcc` and `clang` should both work).
 
 ## Cryptography provider