UI: Fix volume control button styling

The config button and mute checkbox were different sizes.

UI/data/themes/Yami.obt

@@ -1187,9 +1187,10 @@ QSlider::handle:disabled {
 /* Volume Control */
 
 #stackedMixerArea QPushButton {
+    width: var(--icon_base);
+    height: var(--icon_base);
     background-color: var(--button_bg);
-    min-width: var(--icon_base);
-    padding: var(--padding_small) var(--padding_base);
+    padding: var(--padding_base_border) var(--padding_base_border);
     margin: 0px var(--spacing_base);
     border: 1px solid var(--button_border);
     border-radius: var(--border_radius);

UI/volume-control.cpp

@@ -263,9 +263,6 @@ VolControl::VolControl(OBSSource source_, bool showConfig, bool vertical)
 	if (showConfig) {
 		config = new QPushButton(this);
 		config->setProperty("themeID", "menuIconSmall");
-		config->setSizePolicy(QSizePolicy::Maximum,
-				      QSizePolicy::Maximum);
-		config->setMaximumSize(22, 22);
 		config->setAutoDefault(false);
 
 		config->setAccessibleName(