Fixed example 2 so that its runnable (#22328)
Fixed example 2 so that its runnable (#22328)

added some some time consuming code and a return to `CalcDamage`
removed `static` from `CalcTotalDamage` so that the compiler doesn't complain that `CalcDamage` should be static
compiler wasn't happy with `totalDamage += CalcDamage(player);` or `return await Task.WhenAll(totalDamage)` because you are attempting to assign a Task to an int. Fixed it by using `WhenAll` correctly
Changed parameter name of `CalcTotalDamage` from `group` to `people` as  `group` can  be confusing to read as its used with linq
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