test: add comment to all whatwg-url tests
A comment is added to the first line of each whatwg-url test stating that they should not be modified.
Fixes: https://github.com/nodejs/node/issues/12793
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines