fix: wrong is valid if branch

[mattsse]

Closes #2704

the if and else branch were switched, only set idle if valid, else trigger sync.

this would prevent a pipeline fallback if the downloader failed.

[codecov-commenter]

Codecov Report

Merging #2831 (824dd43) into main (2305310) will increase coverage by 12.43%.
The diff coverage is 0.00%.

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@@             Coverage Diff             @@
##             main    #2831       +/-   ##
===========================================
+ Coverage   47.31%   59.74%   +12.43%     
===========================================
  Files         505      505               
  Lines       66162    66168        +6     
===========================================
+ Hits        31305    39533     +8228     
+ Misses      34857    26635     -8222     

Flag	Coverage Δ
integration-tests	17.40% <0.00%> (+<0.01%)	⬆️
unit-tests	54.03% <0.00%> (+13.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
crates/consensus/beacon/src/engine/mod.rs	77.58% <0.00%> (+33.62%)	⬆️
crates/consensus/beacon/src/engine/sync.rs	77.51% <0.00%> (-2.32%)	⬇️

... and 259 files with indirect coverage changes

[rkrasiuk]

gg