Add preview for progressIndicatorTrackColor

Forgot to add it in https://github.com/vector-im/element-x-android/pull/1295

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/theme/ColorAliases.kt

@@ -100,6 +100,7 @@ private fun ContentToPreview() {
             "placeholderBackground" to ElementTheme.colors.placeholderBackground,
             "messageFromMeBackground" to ElementTheme.colors.messageFromMeBackground,
             "messageFromOtherBackground" to ElementTheme.colors.messageFromOtherBackground,
+            "progressIndicatorTrackColor" to ElementTheme.colors.progressIndicatorTrackColor,
             "temporaryColorBgSpecial" to ElementTheme.colors.temporaryColorBgSpecial,
         )
     )