Improve SevenTV tests

[pajlada]

• Add changelog entry
• Add tests for missing emote, bad response

Pull request checklist:

• CHANGELOG.md was updated, if applicable

Description

[codecov]

Codecov Report

Merging #294 (9948395) into master (937c2ec) will increase coverage by 0.46%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #294      +/-   ##
==========================================
+ Coverage   71.32%   71.79%   +0.46%     
==========================================
  Files          56       56              
  Lines        1681     1677       -4     
==========================================
+ Hits         1199     1204       +5     
+ Misses        457      451       -6     
+ Partials       25       22       -3     

Impacted Files	Coverage Δ
internal/resolvers/seventv/emote_loader.go	89.65% <100.00%> (+9.43%)	⬆️

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