🍒kcm/SpeakerTest: Fix the minimum layout for Mono channel

The label needs to set fillWidth: true to influence the sheet's minimum width, so it doesn't get cut out.

This is only noticeable when the grid layout is smaller, when we have single Mono channel. Also slightly adjust the Grid's sizes and alignment for that case

BEFORE	AFTER

BUG: 476096
FIXED-IN: 6.1.4

(cherry picked from commit f3645de3)

3182f64b kcm/SpeakerTest: Fix the minimum layout for Mono channel

Co-authored-by: Ismael Asensio isma.af@gmail.com