style: Fix font-stretch animation.
style: Fix font-stretch animation.

This is a regression from #20506 which Gecko tests caught while trying to import
this.

szeged/servo,cbrewster/servo,paulrouget/servo,sadmansk/servo,nnethercote/servo,larsbergstrom/servo,sadmansk/servo,SimonSapin/servo,jimberlage/servo,peterjoel/servo,emilio/servo,emilio/servo,pyfisch/servo,larsbergstrom/servo,szeged/servo,paulrouget/servo,mbrubeck/servo,pyfisch/servo,peterjoel/servo,paulrouget/servo,splav/servo,ConnorGBrewster/servo,saneyuki/servo,emilio/servo,KiChjang/servo,KiChjang/servo,SimonSapin/servo,peterjoel/servo,dati91/servo,pyfisch/servo,jimberlage/servo,pyfisch/servo,paulrouget/servo,DominoTree/servo,emilio/servo,larsbergstrom/servo,nnethercote/servo,saneyuki/servo,dati91/servo,saneyuki/servo,sadmansk/servo,peterjoel/servo,notriddle/servo,emilio/servo,dati91/servo,splav/servo,szeged/servo,SimonSapin/servo,jimberlage/servo,splav/servo,larsbergstrom/servo,cbrewster/servo,pyfisch/servo,pyfisch/servo,notriddle/servo,cbrewster/servo,saneyuki/servo,SimonSapin/servo,peterjoel/servo,paulrouget/servo,mbrubeck/servo,notriddle/servo,pyfisch/servo,paulrouget/servo,cbrewster/servo,dati91/servo,paulrouget/servo,splav/servo,ConnorGBrewster/servo,DominoTree/servo,splav/servo,KiChjang/servo,SimonSapin/servo,emilio/servo,KiChjang/servo,notriddle/servo,jimberlage/servo,ConnorGBrewster/servo,KiChjang/servo,notriddle/servo,saneyuki/servo,saneyuki/servo,larsbergstrom/servo,jimberlage/servo,notriddle/servo,notriddle/servo,cbrewster/servo,mbrubeck/servo,DominoTree/servo,nnethercote/servo,emilio/servo,sadmansk/servo,szeged/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,saneyuki/servo,nnethercote/servo,mbrubeck/servo,larsbergstrom/servo,nnethercote/servo,sadmansk/servo,ConnorGBrewster/servo,dati91/servo,ConnorGBrewster/servo,szeged/servo,mbrubeck/servo,emilio/servo,pyfisch/servo,notriddle/servo,sadmansk/servo,DominoTree/servo,cbrewster/servo,szeged/servo,mbrubeck/servo,splav/servo,jimberlage/servo,paulrouget/servo,nnethercote/servo,KiChjang/servo,splav/servo,sadmansk/servo,pyfisch/servo,paulrouget/servo,DominoTree/servo,szeged/servo,szeged/servo,larsbergstrom/servo,szeged/servo,KiChjang/servo,SimonSapin/servo,saneyuki/servo,paulrouget/servo,saneyuki/servo,peterjoel/servo,dati91/servo,peterjoel/servo,KiChjang/servo,SimonSapin/servo,dati91/servo,DominoTree/servo,splav/servo,KiChjang/servo,szeged/servo,notriddle/servo,peterjoel/servo,larsbergstrom/servo,KiChjang/servo,nnethercote/servo,jimberlage/servo,DominoTree/servo,emilio/servo,emilio/servo,notriddle/servo,dati91/servo,sadmansk/servo,larsbergstrom/servo,cbrewster/servo,DominoTree/servo,mbrubeck/servo,jimberlage/servo,nnethercote/servo,jimberlage/servo,ConnorGBrewster/servo,mbrubeck/servo,saneyuki/servo,peterjoel/servo,pyfisch/servo,peterjoel/servo,cbrewster/servo,splav/servo,splav/servo,SimonSapin/servo,DominoTree/servo,larsbergstrom/servo,DominoTree/servo,nnethercote/servo,nnethercote/servo