fix(test/fetch): <getter>.call will always throw

[KhafraDev]

The tests would always pass regardless of if the assumption (accessing prototype methods/getters without a valid this value will throw) was correct.

For example,
File.prototype.name is a string, so .call(...) is not a function. It will always throw a TypeError, even if the brand check was removed.

[codecov-commenter]

Codecov Report

Merging #1438 (15582df) into main (1ae6d79) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1438   +/-   ##
=======================================
  Coverage   94.37%   94.37%           
=======================================
  Files          49       49           
  Lines        4231     4231           
=======================================
  Hits         3993     3993           
  Misses        238      238           

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