Add missing header in model solution exercise

changed milestone to %3.7

assigned to @houkili

added 23 commits

• 54e66c50...33d4e2e1 - 22 commits from branch master
• 42cc33cc - Add missing header in model solution exercise

Compare with previous version

enabled an automatic merge when the pipeline for 42cc33cc succeeds

mentioned in commit ffc66a93

merged

picked the changes into the branch cherry-pick-ffc66a93 with commit e27022da

mentioned in commit e27022da

mentioned in merge request !218 (merged)