fix: set text/html content-type when ssr is false (#2059)

Author: huseeiin

.changeset/fifty-flies-yell.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/start": minor
+---
+
+fix text/html missing when ssr is false

packages/start/src/server/handler.ts

@@ -79,6 +79,8 @@ export function createBaseHandler(
           return redirect(context.response.headers.get("Location")!, status);
         }
 
+        event.response.headers.set("content-type", "text/html");
+
         return html;
       }