remove DATABASE_URL from being required for build (#246)

Any questions should be directed to @vujita

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## Breaking Changes

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apps/vubnguyen/src/env.mjs

@@ -1,5 +1,4 @@
 import { createEnv } from "@t3-oss/env-nextjs";
-import { z } from "zod";
 
 export const env = createEnv({
   /**
@@ -22,8 +21,6 @@ export const env = createEnv({
    * Specify your server-side environment variables schema here. This way you can ensure the app isn't
    * built with invalid env vars.
    */
-  server: {
-    DATABASE_URL: z.string().url(),
-  },
+  server: {},
   skipValidation: !!process.env.CI || !!process.env.SKIP_ENV_VALIDATION,
 });