Auto merge of #23402 - servo:jdm-patch-46, r=Manishearth
Auto merge of #23402 - servo:jdm-patch-46, r=Manishearth

Improve output for local WPT sync runs.

This avoids warnings about unset values when running the script locally.

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larsbergstrom/servo,splav/servo,notriddle/servo,larsbergstrom/servo,larsbergstrom/servo,nnethercote/servo,emilio/servo,DominoTree/servo,saneyuki/servo,notriddle/servo,pyfisch/servo,splav/servo,paulrouget/servo,splav/servo,paulrouget/servo,nnethercote/servo,nnethercote/servo,notriddle/servo,DominoTree/servo,KiChjang/servo,paulrouget/servo,DominoTree/servo,nnethercote/servo,nnethercote/servo,KiChjang/servo,paulrouget/servo,pyfisch/servo,saneyuki/servo,emilio/servo,larsbergstrom/servo,DominoTree/servo,splav/servo,nnethercote/servo,pyfisch/servo,pyfisch/servo,KiChjang/servo,saneyuki/servo,DominoTree/servo,notriddle/servo,emilio/servo,emilio/servo,splav/servo,nnethercote/servo,nnethercote/servo,notriddle/servo,splav/servo,pyfisch/servo,saneyuki/servo,emilio/servo,larsbergstrom/servo,KiChjang/servo,splav/servo,pyfisch/servo,splav/servo,paulrouget/servo,splav/servo,larsbergstrom/servo,emilio/servo,splav/servo,saneyuki/servo,KiChjang/servo,KiChjang/servo,paulrouget/servo,paulrouget/servo,saneyuki/servo,paulrouget/servo,emilio/servo,notriddle/servo,notriddle/servo,larsbergstrom/servo,emilio/servo,paulrouget/servo,KiChjang/servo,emilio/servo,DominoTree/servo,larsbergstrom/servo,DominoTree/servo,nnethercote/servo,pyfisch/servo,pyfisch/servo,saneyuki/servo,notriddle/servo,DominoTree/servo,DominoTree/servo,paulrouget/servo,pyfisch/servo,emilio/servo,saneyuki/servo,DominoTree/servo,KiChjang/servo,nnethercote/servo,KiChjang/servo,notriddle/servo,saneyuki/servo,larsbergstrom/servo,pyfisch/servo,KiChjang/servo,notriddle/servo,larsbergstrom/servo,saneyuki/servo