Fix compiler warnings

[hluk]

Fixes unused-result warnings for functions with nodiscard.

Fixes using deprecated QHashCombine without arguments.

[codecov]

Codecov Report

❌ Patch coverage is 52.50000% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.92%. Comparing base (2744902) to head (a29acbb).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/gui/actiondialog.cpp	42.85%	8 Missing ⚠️
src/gui/commanddialog.cpp	0.00%	6 Missing ⚠️
src/app/applicationexceptionhandler.cpp	0.00%	4 Missing ⚠️
src/main.cpp	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3293      +/-   ##
==========================================
- Coverage   79.95%   79.92%   -0.04%     
==========================================
  Files         231      231              
  Lines       28420    28432      +12     
==========================================
+ Hits        22723    22724       +1     
- Misses       5697     5708      +11     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.