doc: clarify use of process.env in worker threads on Windows
A worker thread uses a copy of parent thread's process.env
by default. The current document explains differences caused by the copy, but it doesn't cover the case sensitivity difference on Windows.
This patch updates the document in this regard.
Fixes: #48955 (closed) Alternative to #48976
Signed-off-by: Daeyeon Jeong daeyeon.dev@gmail.com