fix(VChip): correct opacity for plain variant (#22005)

Author: 06b

packages/vuetify/src/components/VChip/_variables.scss

@@ -23,7 +23,7 @@ $chip-label-border-radius: settings.$border-radius-root !default;
 $chip-max-width: 100% !default;
 $chip-overflow: hidden !default;
 $chip-padding-ratio: 2 + math.div(2, 3) !default;
-$chip-plain-opacity: 0.26 !default;
+$chip-plain-opacity: .62 !default;
 $chip-filter-transition: .15s settings.$standard-easing !default;
 $chip-white-space: nowrap !default;