Updating symfony/flex version to [1.13.3](https://packagist.org/packages/symfony/flex#v1.13.3)
Updating symfony/flex version to [1.13.3](https://packagist.org/packages/symfony/flex#v1.13.3)

PiperOrigin-RevId: 387912223
Change-Id: I98a03894dc294ceaca44ebe0e703cdea3eb421e2

GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks,GoogleCloudPlatform/buildpacks