Fix watchfile multiple dev server restart (#12353)

Author: hippotastic

.changeset/famous-timers-move.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue in dev server watch file handling that could cause multiple restarts for a single file change.

packages/astro/src/core/dev/restart.ts

@@ -169,7 +169,9 @@ export async function createContainerWithAutomaticRestart({
 
 		// Restart the Astro dev server instead of Vite's when the API is called by plugins.
 		// Ignore the `forceOptimize` parameter for now.
-		restart.container.viteServer.restart = () => handleServerRestart();
+		restart.container.viteServer.restart = async () => {
+			if (!restart.container.restartInFlight) await handleServerRestart();
+		};
 
 		// Set up shortcuts