Fix archive paths for test packages in the alternative registry

Author: jneem

crates/cargo-test-support/src/registry.rs

@@ -1649,7 +1649,12 @@ impl Package {
     /// Returns the path to the compressed package file.
     pub fn archive_dst(&self) -> PathBuf {
         if self.local {
-            registry_path().join(format!("{}-{}.crate", self.name, self.vers))
+            let path = if self.alternative {
+                alt_registry_path()
+            } else {
+                registry_path()
+            };
+            path.join(format!("{}-{}.crate", self.name, self.vers))
         } else if self.alternative {
             alt_dl_path()
                 .join(&self.name)