Merge branch 'fix/staggered-elemvolvars' into 'master'

Kilian Weishauptrequested to merge
cherry-pick-48ac604b into releases/3.1

[bugfix][staggered] Use value member of true/false_type

See merge request !1783 (merged)

(cherry picked from commit 48ac604b)

dbaad299 [bugfix][staggered] Use value member of true/false_type

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