Optimize factory usage notes helper spec

What does this MR do and why?

This MR replaces create with build_stubbed in ee/spec/helpers/ee/notes_helper_spec.rb to optimize the factory usage as recommended in our handbook.

Average time of 5 runs before update: 14.458000000000002
Average time of 5 runs after the update: 12.492
🚀 Performance improved!
Speedup: 1.97s (13.6% faster)

References

Relates to: #378910.

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