Avoid local variables if not necessary

We can initialize the env filter without `format!` when the variables
are not used anywhere else.

monero-harness/tests/testutils/mod.rs

@@ -7,16 +7,8 @@ use tracing::subscriber::DefaultGuard;
 /// let _guard = init_tracing();
 /// ```
 pub fn init_tracing() -> DefaultGuard {
-    let global_filter = tracing::Level::WARN;
-    let test_filter = tracing::Level::DEBUG;
-    let monero_harness_filter = tracing::Level::DEBUG;
-    let monero_rpc_filter = tracing::Level::DEBUG;
-
     use tracing_subscriber::util::SubscriberInitExt as _;
     tracing_subscriber::fmt()
-        .with_env_filter(format!(
-            "{},test={},monero_harness={},monero_rpc={}",
-            global_filter, test_filter, monero_harness_filter, monero_rpc_filter,
-        ))
+        .with_env_filter("warn,test=debug,monero_harness=debug,monero_rpc=debug")
         .set_default()
 }