fix(mysql): improve compatibility with ProxySQL

Joins the MySQL connection setup statements into a single statement to
prevent issues with ProxySQL, which requires special handling of
connections that might be shared between multiple backends.

Fixes #422

Signed-off-by: Marcus Griep <marcus@griep.us>

sqlx-core/src/mysql/connection/mod.rs

@@ -139,11 +139,11 @@ impl Connect for MySqlConnection {
 
             // https://mathiasbynens.be/notes/mysql-utf8mb4
 
-            conn.execute(r#"
-            SET sql_mode=(SELECT CONCAT(@@sql_mode, ',PIPES_AS_CONCAT,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE'));
-            SET time_zone = '+00:00';
-            SET NAMES utf8mb4 COLLATE utf8mb4_unicode_ci;
-                    "#).await?;
+            conn.execute(concat!(
+                r#"SET sql_mode=(SELECT CONCAT(@@sql_mode, ',PIPES_AS_CONCAT,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE')),"#,
+                r#"time_zone='+00:00',"#,
+                r#"NAMES utf8mb4 COLLATE utf8mb4_unicode_ci;"#,
+            )).await?;
 
             Ok(conn)
         })