testing/slogtest: reword a confusing explanation

Updates golang#61758.

Change-Id: I4ce0359f676b6832e40203e1034ba1c4f6d2b2ed
Reviewed-on: https://go-review.googlesource.com/c/go/+/516155
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Patrick Ohly <patrick.ohly@googlemail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/testing/slogtest/slogtest.go

@@ -163,7 +163,7 @@ func TestHandler(h slog.Handler, results func() []map[string]any) error {
 			},
 		},
 		{
-			explanation: withSource("a Handler should not output groups for an empty Record"),
+			explanation: withSource("a Handler should not output groups if there are no attributes"),
 			f: func(l *slog.Logger) {
 				l.With("a", "b").WithGroup("G").With("c", "d").WithGroup("H").Info("msg")
 			},