test: avoid random fail in test_rfc_index

[jennifer-richards]

The test_rfc_index test fails if the WgDraftFactory happens to choose pages=42. This ensures it doesn't.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.34%. Comparing base (8005a8b) to head (d0f299e).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10469      +/-   ##
==========================================
- Coverage   88.36%   88.34%   -0.03%     
==========================================
  Files         325      326       +1     
  Lines       43653    43744      +91     
==========================================
+ Hits        38576    38645      +69     
- Misses       5077     5099      +22     

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