docs(mutmut): fix line-number drift on item E mutant 17 (QA-caught)

qa-reviewer caught that the item E doc claimed mutant 17 was at

bin/wl_audit.py:88, but the actual mutated line is 91. Line 88 is

blank whitespace; the kwarg filter

  if key not in ("app_context", "comment"):

is at line 91.

Cause: I conflated the diff hunk's starting line (the '@@ -88,7 +88,7'

header from mutmut show) with the actual mutated line within that

hunk. The hunk starts at line 88 and shows 7 lines of context;

the mutated line is the 4th line shown, so line 91.

Verified the other two mutants from the same section:

  - Mutant 55 at line 156: confirmed (line 155 is

    'req = urllib.request.Request(...)'; line 156 is the

    add_header line — matches doc)

  - Mutant 88 at line 189: confirmed ('error_msg = str(e)' at 189)

Only mutant 17 needed fixing.

doc-drift: OK (33 docs against build 660).

Author: RelativisticJet

docs/MUTATION_TESTING.md

@@ -317,7 +317,7 @@ into 4 classes:
 
 ### Higher-value survivors (deferred to item G)
 
-- **Mutant 17** (line 88): kwarg filter `("app_context", "comment")`
+- **Mutant 17** (line 91): kwarg filter `("app_context", "comment")`
   → `("XXapp_contextXX", "comment")`. Mutated version doesn't filter
   `app_context`, so it would be added to the event dict redundantly
   with the explicit `event["app_context"] = ...` write earlier. The