fix: clippy warnings with --all-features (#15035)

# Description

Some more `cargo clippy --all-features` warnings from rust toolchain
1.84.1 that I forgot to fix in #14984

crates/nu-test-support/src/playground/play.rs

@@ -52,7 +52,7 @@ impl Dirs {
     }
 }
 
-impl<'a> Playground<'a> {
+impl Playground<'_> {
     pub fn root(&self) -> &AbsolutePath {
         &self.dirs.root
     }