[`flake8-pie`] Small docs fix to `PIE794` (#18829)
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## Summary
<!-- What's the purpose of the change? What does it do, and why? -->
I noticed this since my code for finding missing safety fix sections
flagged it, there is a missing `/` causing part of the new changes to be
a normal comment instead of a doc comment
## Test Plan
<!-- How was it tested? -->
N/A, no functionality/tests affected
