List of `libicu` versions in Debian DEPS file needs occasional updates

[NikolaMilosavljevic]

We've had to update the list of supported libicu versions several times in the past. Latest one: #115374

It would be best if we don't need to touch this file manually and have a way to automatically add latest and some future versions.

One suggested solution: #115378 (comment)

[NikolaMilosavljevic]

[Triage] @NikolaMilosavljevic please investigate this and come up with a solution. Per @MichaelSimons we could at least have a unit-test to discover latest libicu version in distro's latest docker images (not .NET modified ones) and compare with some property in our infra.