Enable frozen string for some vestigial app/ files
Turns out false satisfies the cop as well.
xref:
https://github.com/rubocop-hq/rubocop/issues/7241
https://github.com/rubocop-hq/rubocop/issues/7426
cc @tkuah
cc @nick.thomas (you authored gitlab-foss!25432 (merged))
Edited by gfyoung