Speed up @apply migration test

Author: thecrypticace

packages/@tailwindcss-upgrade/src/codemods/css/migrate-at-apply.test.ts

@@ -13,6 +13,11 @@ async function migrate(input: string, config: Config = {}) {
   let designSystem = await __unstable__loadDesignSystem(
     css`
       @import 'tailwindcss';
+
+      /* TODO(perf): Only here to speed up the tests */
+      @theme {
+        --*: initial;
+      }
     `,
     { base: __dirname },
   )
@@ -96,6 +101,10 @@ it(
             designSystem: await __unstable__loadDesignSystem(
               css`
                 @import 'tailwindcss' prefix(tw);
+                /* TODO(perf): Only here to speed up the tests */
+                @theme {
+                  --*: initial;
+                }
               `,
               { base: __dirname },
             ),