Fix calendar shifts when First day of the week is enabled ( #2761)

[AAraKKe]

GitHub Issue (if applicable): #2761

Explanation of Bugfix/Feature/Modification:
I modified where the tkShifted data attribute is added to allow the guard supplied to the onElement method to work since the querySelector will return null if the attribute is in the same element where we are querying.

[joshmadewell]

ah yeah...i made onElement (this is such a bad name, plz no judge lol) look at the element passed in after i'd already fixed this feature with it....honestly...I think I should maybe change that back to just checking the dom :( either way...i'll take this PR for now and update if needed. thanks!