Fix "last good" link introduced in 8fc2dc99a

[okurz]

Related progress issue: https://progress.opensuse.org/issues/69085

[Martchus]

Looks good. Note that using the url_for helper would likely be the best (or at least designated) way to make this.

[codecov]

Codecov Report

Merging #3284 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3284      +/-   ##
==========================================
- Coverage   91.51%   91.50%   -0.01%     
==========================================
  Files         215      215              
  Lines       13064    13064              
==========================================
- Hits        11955    11954       -1     
- Misses       1109     1110       +1     

Impacted Files	Coverage Δ
lib/OpenQA/Schema/Result/Jobs.pm	97.68% <ø> (ø)
lib/OpenQA/WebSockets.pm	85.71% <0.00%> (-3.18%)	⬇️
lib/OpenQA/WebAPI/Plugin/Helpers.pm	95.91% <0.00%> (+0.40%)	⬆️

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[okurz]

I was thinking of url_for as well, maybe as a follow-up