make integration tests Julia version for each project configureable

[SimeonEhrig]

At the moment, the Julia version for integration tests is hard coded to version 1.9. The version should be optional adjustable per project. The idea is, that the version can be set as environment variable in the generator job of the .gitlab-ci.yaml of the project, which generates the integration tests. If the variable is not set, there will be a fallback version, for example 1.9.

[AntonReinhard]

Should this issue be moved to https://github.com/QEDjl-project/IntegrationTests.jl ?