build: add cargo component to rust-toolchain.toml

I noticed that when I force-updated the toolchain being used for wgpu,
I got an error about the `cargo` binary not being available after
redirecting a naive `cargo` invocation to the set of binaries for the
1.93 toolchain. This fixes that issue.

Author: ErichDonGubler

rust-toolchain.toml

@@ -1,4 +1,4 @@
 [toolchain]
 channel = "1.93"
-components = ["rustfmt", "clippy"]
+components = ["cargo", "rustfmt", "clippy"]
 targets = ["wasm32-unknown-unknown"]