Skip python_install_emulated_macos except on ARM64 macos with rosetta (#16687)

## Summary

This test isn't useful on non-arm64 macs, and it outright fails if
rosetta isn't installed.

## Test Plan

Run it on my rosetta-stripped macbook

crates/uv/tests/it/python_install.rs

@@ -2694,7 +2694,7 @@ fn python_install_no_cache() {
     ");
 }
 
-#[cfg(target_os = "macos")]
+#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
 #[test]
 fn python_install_emulated_macos() {
     let context: TestContext = TestContext::new_with_versions(&[])
@@ -2702,6 +2702,20 @@ fn python_install_emulated_macos() {
         .with_managed_python_dirs()
         .with_python_download_cache();
 
+    let arch_status = Command::new("/usr/bin/arch")
+        .arg("-x86_64")
+        .arg("true")
+        .status();
+    if !arch_status.is_ok_and(|x| x.success()) {
+        // Rosetta is not available to run the x86_64 interpreter
+        // fail the test in CI, otherwise skip it
+        if env::var("CI").is_ok() {
+            panic!("x86_64 emulation is not available on this CI runner");
+        }
+        debug!("Skipping test because x86_64 emulation is not available");
+        return;
+    }
+
     // Before installation, `uv python list` should not show the x86_64 download
     uv_snapshot!(context.filters(), context.python_list().arg("3.13"), @r"
     success: true