fix(progressbar): enforce staticWhite track color

this removes the previously created mod property that could override the
staticWhite background-color, which is in contradiction to how the CSS
should behave.

Author: marissahuysentruyt

components/progressbar/index.css

@@ -235,7 +235,7 @@
 	}
 
 	.spectrum-ProgressBar-track {
-		background: var(--mod-progressbar-track-color-white, var(--spectrum-progressbar-track-color-white));
+		background-color: var(--spectrum-progressbar-track-color-white);
 	}
 }
 

components/progressbar/stories/template.js

@@ -54,7 +54,8 @@ export const Template = ({
 
 			<div
 				class="${rootClass}-track"
-				style="--mod-progressbar-track-color: ${ifDefined(trackFill)}">
+				style="--mod-progressbar-track-color: ${staticColor !== "white" ? ifDefined(trackFill) : undefined}"
+			>
 				<div
 					class="${rootClass}-fill"
 					style=