test(backdrop): add test for backdrop store

[camc314]

Adds Tests for:

• committing 'SET_CURRENT_BACKDROP'
• committing 'CLEAR_CURRENT_BACKDROP'
• dispatching 'setBackdrop'
• dispatching 'clearBackdrop'
• gettter 'getBackdropBlurhash'

[ferferga]

@camc314 Backdrop store is completely refactored on #520, the fixes that you're applying here are already there. You can rebase the commit without your changes in it, so no need to fix conflicts later.

[camc314]

I'll rebase on 520

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities
0 Security Hotspots
2 Code Smells

No Coverage information
0.0% Duplication

[camc314]

Rebased and ready for review

[codecov-io]

Codecov Report

Merging #532 (ad8fc2b) into master (381b061) will increase coverage by 0.75%.
The diff coverage is 75.00%.

@@            Coverage Diff            @@
##           master    #532      +/-   ##
=========================================
+ Coverage    2.23%   2.99%   +0.75%     
=========================================
  Files          97      97              
  Lines        2635    2635              
  Branches      417     417              
=========================================
+ Hits           59      79      +20     
+ Misses       2574    2553      -21     
- Partials        2       3       +1     

Impacted Files	Coverage Δ
components/Layout/HomeHeader/HomeHeaderItems.vue	0.00% <ø> (ø)
pages/playback/index.vue	0.00% <0.00%> (ø)
store/backdrop.ts	83.33% <100.00%> (+83.33%)	⬆️

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