ci: Install pre-built cargo nextest instead of rolling our own (#42556)

Closes #ISSUE

Release Notes:

- N/A

tooling/xtask/src/tasks/workflows/run_agent_evals.rs

@@ -126,7 +126,7 @@ fn unit_evals(commit: Option<&Input>) -> Job {
         .add_step(steps::setup_cargo_config(Platform::Linux))
         .add_step(steps::cache_rust_dependencies_namespace())
         .map(steps::install_linux_dependencies)
-        .add_step(steps::cargo_install_nextest(Platform::Linux))
+        .add_step(steps::cargo_install_nextest())
         .add_step(steps::clear_target_dir_if_large(Platform::Linux))
         .add_step(match commit {
             Some(commit) => script_step.add_env(("UNIT_EVAL_COMMIT", commit)),

tooling/xtask/src/tasks/workflows/run_tests.rs

@@ -321,7 +321,9 @@ pub(crate) fn run_platform_tests(platform: Platform) -> NamedJob {
             )
             .add_step(steps::setup_node())
             .add_step(steps::clippy(platform))
-            .add_step(steps::cargo_install_nextest(platform))
+            .when(platform == Platform::Linux, |job| {
+                job.add_step(steps::cargo_install_nextest())
+            })
             .add_step(steps::clear_target_dir_if_large(platform))
             .add_step(steps::cargo_nextest(platform))
             .add_step(steps::cleanup_cargo_config(platform)),

tooling/xtask/src/tasks/workflows/steps.rs

@@ -48,8 +48,8 @@ pub fn cargo_fmt() -> Step<Run> {
     named::bash("cargo fmt --all -- --check")
 }
 
-pub fn cargo_install_nextest(platform: Platform) -> Step<Run> {
-    named::run(platform, "cargo install cargo-nextest --locked")
+pub fn cargo_install_nextest() -> Step<Use> {
+    named::uses("taiki-e", "install-action", "nextest")
 }
 
 pub fn cargo_nextest(platform: Platform) -> Step<Run> {