Fix 'show source [in new tab]' under -lines

[tbg]

With this patch, it's possible to navigate from the (new and now only) flame graph to the source code for a box.

[aalexand]

Could you add a comment that explains the "why" behind the regexp? (no need to explain the regexp mechanics itself)

[tbg]

Sure, done!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.97%. Comparing base (0ed6a68) to head (8149a29).
Report is 55 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #912      +/-   ##
==========================================
+ Coverage   66.86%   66.97%   +0.10%     
==========================================
  Files          44       44              
  Lines        9824     9855      +31     
==========================================
+ Hits         6569     6600      +31     
- Misses       2794     2816      +22     
+ Partials      461      439      -22     

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[tbg]

Thanks @aalexand - could you merge?