Fix incorrect debug message

Dependencies

• [2] HUUZFPPK Fix race between the queue monitor and the builder threads
• [3] 24BMQDZA Start of single-process hydra-queue-runner
• [4] 63W4T5PU hydra-queue-runner: More stats

Change contents

• replacement in src/hydra-queue-runner/hydra-queue-runner.cc at line 1272
  [2.6517]→[2.6517:6619](∅→∅)
  − printMsg(lvlDebug, format("finishing build step ‘%1%’") % step->drvPath);
  [2.6517]

  [2.6658]
  + printMsg(lvlDebug, format("finishing build step ‘%1%’") % s->drvPath);