Cargo: bump MSRV to 1.71

Our dependency `env_logger` suffers from a bug in versions of Cargo
older than 1.71, fixed by rust-lang/cargo#12130
(the one we suffered from before the "Cargo: don't let feature
"static" pull xenstore-rs unless "xenstore" is set" fix).

Note that some of our dependencies already required 1.70 or later.

Signed-off-by: Yann Dirson <yann.dirson@vates.fr>

Cargo.toml

@@ -3,7 +3,7 @@ name = "xen-guest-agent"
 version = "0.5.0-dev"
 authors = ["Yann Dirson <yann.dirson@vates.fr>"]
 edition = "2018"
-rust-version = "1.64"
+rust-version = "1.71"
 license = "AGPL-3.0-only"
 
 [dependencies]

README.md

@@ -40,8 +40,7 @@ Some features to consider (from `xe-guest-utilities`):
 
 ### Build requirements
 
-You need a Rust toolchain.  Some of our dependencies require Rust
-1.70 or later.
+You need a Rust 1.71 toolchain or later.
 
 Since the Cargo tool cannot be told about non-Rust dependencies, you
 have to install manually on your build machine: