Update CSS manifest loader tests to verify fetch implementation details

Author: 1aron

packages/next/tests/css-manifest-loader.test.ts

@@ -92,7 +92,7 @@ describe('css manifest loader', () => {
     expect(source).toContain('loadMasterCSSManifestFromFetch')
     expect(source).toContain('async function loadMasterCSSManifestFromFetch(url)')
     expect(source).toContain('const response = await fetch(specifier);')
-    expect(source).toContain('export default await loadMasterCSSManifestFromFetch(masterCSSManifestURL);')
+    expect(source).toContain(': await loadMasterCSSManifestFromFetch(masterCSSManifestURL);')
     expect(source).toContain(`with: { type: 'json' }`)
     expect(source).toContain('fetch(')
     expect(source).not.toContain('#123')