fixup! hydra-notify: pre-declare metrics

Dependencies

• [2] BJJLHGFC hydra-notify: pre-declare metrics
• [3] 4H6FVIWG hydra-notify: make the prometheus endpoint configurable, default-off
• [*] IE2PRAQU hydra-queue-runner: Send build notifications

Change contents

• replacement in src/script/hydra-notify at line 25
  [2.75]→[2.75:136](∅→∅)
  − # Add a new declaration for any new metrics you create. See:
  [2.75]

  [2.136]
  + # Add a new declaration for any new metrics you create. Metrics which are

  + # not pre-declared disappear when their value is null. See: