[Ellen's Alien Game] Test that an instance variable is used for the health, not a class variable.

[IsaacG]

No description provided.

[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

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[IsaacG]

This solution uses a class var for the health. It passes the existing tests and fails this new test.