RailML importer bug fix: reset importer between consecutive train import

MANDATORY

• Fill in the JIRA ticket
• Rebase current branch onto sprint (example : git rebase -i 3.11/sprint)
• Test of the rebased version (all unit tests / manual tests only for the issue)
• If needed, add or update Confluence documentation (except for bug fixes)
• If needed, update the next release page : https://moviplus.atlassian.net/wiki/spaces/SYN/pages/287342640/Prochaine+version

OPTIONAL

• If it’s a feature story, the PO saw the result and gave the GO for merge