According to the tests, Project::putInTrash doesnt work

Please, fix the method Project::putInTrash :

java.util.ConcurrentModificationException
    at java.base/java.util.ArrayList.forEach(ArrayList.java:1513)
    at fr.alma.gtd.server.core.AbstractProject.putInTrash(AbstractProject.java:119)
    at fr.alma.gtd.server.main.donnees.ProjectTest.testIsTrash(ProjectTest.java:172)