Edit.php: wikify: fix link regex (page titles cannot contain []s)

[agoujot]

Does exactly what it says on the tin.

Given how trivial and self-evident this is, i'm self-merging

Bug: T408332

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.47%. Comparing base (4b8eb28) to head (a22307e).
⚠️ Report is 184 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #581      +/-   ##
============================================
- Coverage     71.30%   69.47%   -1.84%     
- Complexity     1275     1326      +51     
============================================
  Files            46       46              
  Lines          3792     3921     +129     
============================================
+ Hits           2704     2724      +20     
- Misses         1088     1197     +109     

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