Replace set_var usage in examples (#829)

* examples: Fix inconsistent toml formatting

* examples: Replace set_var usage

examples/sqlx-postgres/src/main.rs

@@ -21,16 +21,18 @@ use axum::{
     Router,
 };
 use sqlx::postgres::{PgPool, PgPoolOptions};
+use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};
 
 use std::{net::SocketAddr, time::Duration};
 
 #[tokio::main]
 async fn main() {
-    // Set the RUST_LOG, if it hasn't been explicitly defined
-    if std::env::var_os("RUST_LOG").is_none() {
-        std::env::set_var("RUST_LOG", "example_tokio_postgres=debug")
-    }
-    tracing_subscriber::fmt::init();
+    tracing_subscriber::registry()
+        .with(tracing_subscriber::EnvFilter::new(
+            std::env::var("RUST_LOG").unwrap_or_else(|_| "example_tokio_postgres=debug".into()),
+        ))
+        .with(tracing_subscriber::fmt::layer())
+        .init();
 
     let db_connection_str = std::env::var("DATABASE_URL")
         .unwrap_or_else(|_| "postgres://postgres:password@localhost".to_string());