Fix type of OverrideSpecifier.vOverrides to comply with type of child nodes

[blitz-1306]

No description provided.

[blitz-1306]

Overall, this fix should be more extensive, as we should tweak ASTNodeWithChildren to respect children type T more properly (ownChildren should be of type T instead of ASTNode, all relevant methods should be tuned).

[codecov-commenter]

Codecov Report

Merging #236 (8cd0be3) into master (a7344e5) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #236   +/-   ##
=======================================
  Coverage   91.59%   91.59%           
=======================================
  Files         267      267           
  Lines        6630     6630           
  Branches     1353     1353           
=======================================
  Hits         6073     6073           
  Misses        291      291           
  Partials      266      266           

Files	Coverage Δ
src/ast/implementation/meta/override_specifier.ts	100.00% <100.00%> (ø)

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