docs: fix env variable name notification(s)-delay

[kirbylink]

Setting correct env. variable for --notifications-delay in notifications.md
See #1485

[github-actions]

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[codecov]

Codecov Report

Base: 64.76% // Head: 64.76% // No change to project coverage 👍

Coverage data is based on head (3af096f) compared to base (d5d711b).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1486   +/-   ##
=======================================
  Coverage   64.76%   64.76%           
=======================================
  Files          24       24           
  Lines        2310     2310           
=======================================
  Hits         1496     1496           
  Misses        718      718           
  Partials       96       96           

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[Tentoe]

It's an S and it is correct.
How is it not merged yet?

[piksel]

Yeah, I don't know. Must've missed it.