Write all logging (INFO, WARN, ERROR) to stderr

The old setup tried to log >= warning to stderr, the rest to stdout.

However, that logic was flawed, so warnings ended up in stdout, which makes `hugo list all` etc. hard to reason about from scripts.

This commit fixes this by making all logging (info, warn, error) log to stderr and let stdout be reserved for program output.

Fixes #13074

common/loggers/handlerterminal.go

@@ -40,8 +40,8 @@ func newNoAnsiEscapeHandler(outWriter, errWriter io.Writer, noLevelPrefix bool,
 
 type noAnsiEscapeHandler struct {
 	mu            sync.Mutex
-	outWriter     io.Writer // Defaults to os.Stdout.
-	errWriter     io.Writer // Defaults to os.Stderr.
+	outWriter     io.Writer
+	errWriter     io.Writer
 	predicate     func(*logg.Entry) bool
 	noLevelPrefix bool
 }