test: increase coverage for fs/dir read
test invalid callback case for fs/dir read
Refs: https://coverage.nodejs.org/coverage-f7dd330ba0e7bfa9/lib/internal/fs/dir.js.html#L91
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines