Update to latest flutter version

[niclas-lindgren]

Current version of the image is 3.16.3.
Latest version is 3.19.1

There are breaking changes for integration_tests that depends in file 6.x in version 3.16 while it depends on 7.x in 3.19

[bartekpacia]

You can try this image instead: https://github.com/cirruslabs/docker-images-flutter