fix(downloads): allow the deliberate join_absolute_paths lint in a test

The assertion documents that PathBuf::join discards its base when handed an
absolute path — which is why confinement has to happen after the join, not
instead of it. clippy::join_absolute_paths flags that shape, correctly for
production code, so the lint is allowed here rather than the test weakened.

Worth recording: this lint would not have caught the original defect. The real
join sites pass a variable, and it only fires on a literal.

src-tauri/src/commands/download/mod.rs

@@ -2568,10 +2568,19 @@ mod tests {
 
         // Why the absolute case needs its own guard rather than folding: the
         // join the download path performs discards the base entirely.
-        assert_eq!(
-            PathBuf::from(root).join("/etc/cron.d/pwn"),
-            PathBuf::from("/etc/cron.d/pwn")
-        );
+        //
+        // clippy::join_absolute_paths flags exactly this shape, and is right to
+        // in production code — here the discarded base *is* the assertion, so
+        // the lint is allowed rather than the code changed. Note the lint would
+        // not have caught the original defect: the real join sites take a
+        // variable, and the lint only fires on a literal starting with `/`.
+        #[allow(clippy::join_absolute_paths)]
+        {
+            assert_eq!(
+                PathBuf::from(root).join("/etc/cron.d/pwn"),
+                PathBuf::from("/etc/cron.d/pwn")
+            );
+        }
     }
 
     /// The paths the app builds for itself have to survive unchanged: files are