Fix end to end wait_for_the_expected_time test

[jpraynaud]

Issue

Fix the end to end test that fails on nix:

---- utils::spec_utils::tests::wait_for_the_expected_time stdout ----
thread 'utils::spec_utils::tests::wait_for_the_expected_time' panicked at 'Failure, after one loop the elapsed time was not ~10ms, elapsed: 19', mithril-test-lab/mithril-end-to-end/src/utils/spec_utils.rs:99:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

See https://github.com/input-output-hk/mithril/runs/16169110118