chore: remove one assertion

Author: sapphi-red

playground/js-sourcemap/__tests__/js-sourcemap.spec.ts

@@ -191,10 +191,6 @@ describe.runIf(isBuild)('build tests', () => {
       const mapObj = JSON.parse(mapContent)
 
       if (mapObj.file) {
-        expect(
-          mapObj.file,
-          `Sourcemap file field for ${mapAsset} should not include directory prefix`,
-        ).not.toMatch(/^assets\//)
         expect(
           mapObj.file,
           `Sourcemap file field for ${mapAsset} should be just the filename`,