Merge bitcoin/bitcoin#30010: lint: [doc] Clarify Windows line endings (CR LF) not to be used

fa9be2f lint: [doc] Clarify Windows line endings (CR LF) not to be used (MarcoFalke)

Pull request description:

  It has been this case since the linter was introduced years ago. Given a misunderstanding (bitcoin/bitcoin#28074 (comment)), clarify the docs.

ACKs for top commit:
  brunoerg:
    ACK fa9be2f

Tree-SHA512: be714db9df533e0962ed84102ffdb72717902949b930d58cf5a79cba36297f6b2b1f75e65a2c1f46bcb8e2f4ad5d025f3d15210f468a5ec9631a580b74f923ea

Author: fanquake

test/lint/test_runner/src/main.rs

@@ -137,9 +137,9 @@ fn lint_trailing_whitespace() -> LintResult {
     if trailing_space {
         Err(r#"
 ^^^
-Trailing whitespace is problematic, because git may warn about it, or editors may remove it by
-default, forcing developers in the future to either undo the changes manually or spend time on
-review.
+Trailing whitespace (including Windows line endings [CR LF]) is problematic, because git may warn
+about it, or editors may remove it by default, forcing developers in the future to either undo the
+changes manually or spend time on review.
 
 Thus, it is best to remove the trailing space now.