fix clippy (#10659)

This pr fix clippy warnings in latest clippy version(1.72.0):

Unfortunally it's not easy to handle for [try
fold](https://rust-lang.github.io/rust-clippy/master/index.html#/manual_try_fold)
warning in `start command`

Refer to known issue:
> This lint doesn’t take into account whether a function does something
on the failure case, i.e., whether short-circuiting will affect
behavior. Refactoring to try_fold is not desirable in those cases.

That's the case for our code, which does something on the failure case.

So this pr is making a little refactor on `try_commands`.

crates/nu-test-support/src/fs.rs

@@ -233,7 +233,7 @@ pub fn root() -> PathBuf {
 }
 
 pub fn binaries() -> PathBuf {
-    let build_target = std::env::var("CARGO_BUILD_TARGET").unwrap_or(String::new());
+    let build_target = std::env::var("CARGO_BUILD_TARGET").unwrap_or_default();
 
     let profile = if let Ok(env_profile) = std::env::var("NUSHELL_CARGO_PROFILE") {
         env_profile

crates/nu-test-support/src/macros.rs

@@ -212,6 +212,7 @@ macro_rules! nu_with_plugins {
 }
 
 use crate::{Outcome, NATIVE_PATH_ENV_VAR};
+use std::fmt::Write;
 use std::{
     path::Path,
     process::{Command, Stdio},
@@ -299,14 +300,14 @@ pub fn nu_with_plugin_run_test(cwd: impl AsRef<Path>, plugins: &[&str], command:
 
     let registrations: String = plugins
         .iter()
-        .map(|plugin_name| {
+        .fold(String::new(), |mut output, plugin_name| {
             let plugin = with_exe(plugin_name);
             let plugin_path = nu_path::canonicalize_with(&plugin, &test_bins)
                 .unwrap_or_else(|_| panic!("failed to canonicalize plugin {} path", &plugin));
             let plugin_path = plugin_path.to_string_lossy();
-            format!("register {plugin_path};")
-        })
-        .collect();
+            let _ = write!(output, "register {plugin_path};");
+            output
+        });
     let commands = format!("{registrations}{command}");
 
     let target_cwd = crate::fs::in_directory(&cwd);