find: Add --set as alias of --write-msrv

Introduce --set as an alias for the --write-msrv option in `cargo msrv
find' to maintain consistency with `cargo msrv set'.

Closes #1047.

src/cli/mod.rs

@@ -164,7 +164,7 @@ pub struct FindOpts {
     /// For toolchains which include a Cargo version which supports the rust-version field,
     /// the `package.rust-version` field will be written. For older Rust toolchains,
     /// the `package.metadata.msrv` field will be written instead.
-    #[arg(long)]
+    #[arg(long, alias = "set")]
     pub write_msrv: bool,
 
     #[command(flatten)]