fix: back button invisible for some preferences' screen

[g123k]

The back button is visible again 🥳

Fix #2756

[codecov-commenter]

Codecov Report

Merging #2760 (d75bf26) into develop (2ea0da3) will decrease coverage by 1.69%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop   #2760      +/-   ##
==========================================
- Coverage     8.86%   7.16%   -1.70%     
==========================================
  Files          161     218      +57     
  Lines         6623   10565    +3942     
==========================================
+ Hits           587     757     +170     
- Misses        6036    9808    +3772     

Impacted Files	Coverage Δ
...kages/smooth_app/lib/widgets/attribute_button.dart	0.00% <0.00%> (-92.00%)	⬇️
...s/smooth_app/lib/data_models/user_preferences.dart	8.73% <0.00%> (-23.57%)	⬇️
packages/smooth_app/lib/themes/smooth_theme.dart	62.26% <0.00%> (-20.72%)	⬇️
...p/lib/generic_lib/dialogs/smooth_alert_dialog.dart	15.11% <0.00%> (-19.10%)	⬇️
...mooth_app/lib/data_models/product_preferences.dart	21.68% <0.00%> (-9.75%)	⬇️
packages/smooth_app/lib/main.dart	14.65% <0.00%> (-3.24%)	⬇️
.../smooth_app/lib/pages/onboarding/welcome_page.dart	0.00% <0.00%> (-3.13%)	⬇️
.../smooth_app/lib/pages/onboarding/scan_example.dart	0.00% <0.00%> (-2.28%)	⬇️
...p/lib/pages/onboarding/consent_analytics_page.dart	0.00% <0.00%> (-1.57%)	⬇️
...ackages/smooth_app/lib/pages/scan/scan_header.dart	3.33% <0.00%> (-1.43%)	⬇️
... and 237 more

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[M123-dev]

LGTM, thanks @g123k