README.activity-report: Replace new editors appointment (June).

* README.activity-report: Update.

README.activity-report

@@ -128,7 +128,7 @@ _Note_: See https://hal.science/search/index?q=Guix-HPC+Activity+Report for
 *** TODO guix-science@gnu.org
 *** TODO your favorite mailing lists
 ** TODO **February** Print hard copies of the booklet to distribute at relevant venues
-** TODO **September**: Appoint the new Editors; preferably two;
+** TODO **June**: Appoint the new Editors; preferably two;
 
 * _Notes_