`Command::cargo_bin` is deprecated... and is used in several examples

[ahl]

Some examples:

assert_cmd/README.md

Lines 15 to 22 in ee88946

	Here's a trivial example:
	```rust,no_run
	use assert_cmd::Command;
	let mut cmd = Command::cargo_bin("bin_fixture").unwrap();
	cmd.assert().success();
	```

assert_cmd/src/lib.rs

Lines 48 to 63 in ee88946

	//! And a little of everything:
	//! ```rust,no_run
	//! use assert_cmd::Command;
	//!
	//! let mut cmd = Command::cargo_bin("bin_fixture").unwrap();
	//! let assert = cmd
	//! .arg("-A")
	//! .env("stdout", "hello")
	//! .env("exit", "42")
	//! .write_stdin("42")
	//! .assert();
	//! assert
	//! .failure()
	//! .code(42)
	//! .stdout("hello\n");
	//! ```

assert_cmd/src/cargo.rs

Lines 6 to 19 in ee88946

	//! # Examples
	//!
	//! Simple case:
	//!
	//! ```rust,no_run
	//! use assert_cmd::prelude::*;
	//! use assert_cmd::pkg_name;
	//!
	//! use std::process::Command;
	//!
	//! let mut cmd = Command::cargo_bin(pkg_name!())
	//! .unwrap();
	//! let output = cmd.unwrap();
	//! ```

Perhaps beyond the scope of this issue, but I haven't been able to make use of the proposed alternatives to Command::cargo_bin:
https://github.com/oxidecomputer/oxide.rs/blob/06f4a01170f2decf81d4d39ca3a5f02a3c5345a6/cli/src/cmd_auth.rs#L651-L663

In particular, we're using this in a unit test which appears to be either something that worked by accident or a newly broken use case.

[epage]

Not updating the documentation was acknowledged in #248. We can't get the examples to compile otherwise because the environment variable is not set on the doctest process. Making all examples skip being doctests leads to problems like #249.

So I'm going to close for now. Likely the ideal solution would be to move the env variables from being set at compile time to also being set at runtime within cargo.

[ahl]

Our use (i.e. that mimics those examples) is in unit tests where the environment variable isn't set. Is the only recourse to move those to integration tests?

[epage]

Our use (i.e. that mimics those examples) is in unit tests where the environment variable isn't set. Is the only recourse to move those to integration tests?

cargo test does not ensure the binary is available for unit tests and you can get stale copies of the binary (and be very confused). We document that you should only use it in integration tests at https://docs.rs/assert_cmd/latest/assert_cmd/cargo/index.html#limitations which is linked to from the different functions.