deps: update librustls 0.12.0 -> 0.13.0

This commit updates the optional rustls-ffi librustls dependency from
0.12.0 to 0.13.0. This version is based on the latest available rustls
release (0.23.4).

The breaking API changes from 0.12.0 to 0.13.0 are in API surface unused
by curl, so this is an in-place update without any code changes.

The `RUSTLS.md` documentation is updated to reflect the new version in
use, and to clarify that `cbindgen` isn't required to build `librustls`
- it's only used by developers to update the vendored `rustls.h` header
file maintained upstream.

Closes #13238

.github/workflows/linux.yml

@@ -48,7 +48,7 @@ env:
   msh3-version: v0.6.0
   openssl3-version: openssl-3.1.3
   quictls-version: 3.1.4+quic
-  rustls-version: v0.12.0
+  rustls-version: v0.13.0
 
 jobs:
   autotools:

docs/RUSTLS.md

@@ -3,7 +3,7 @@
 [Rustls is a TLS backend written in Rust](https://docs.rs/rustls/). Curl can
 be built to use it as an alternative to OpenSSL or other TLS backends. We use
 the [rustls-ffi C bindings](https://github.com/rustls/rustls-ffi/). This
-version of curl depends on version v0.12.0 of rustls-ffi.
+version of curl depends on version v0.13.0 of rustls-ffi.
 
 # Building with rustls
 
@@ -11,8 +11,7 @@ First, [install Rust](https://rustup.rs/).
 
 Next, check out, build, and install the appropriate version of rustls-ffi:
 
-    % cargo install cbindgen
-    % git clone https://github.com/rustls/rustls-ffi -b v0.12.0
+    % git clone https://github.com/rustls/rustls-ffi -b v0.13.0
     % cd rustls-ffi
     % make
     % make DESTDIR=${HOME}/rustls-ffi-built/ install