Updating dark outlineVariant to be visible against dark surfaceVariant

Author: FelberMartin

app/src/main/java/de/tum/informatics/www1/artemis/native_app/android/ui/Color.kt

@@ -61,7 +61,7 @@ val md_theme_dark_inverseSurface = Color(0xFFE2E2E5)
 val md_theme_dark_inversePrimary = Color(0xFF006398)
 val md_theme_dark_shadow = Color(0xFF000000)
 val md_theme_dark_surfaceTint = Color(0xFF93CCFF)
-val md_theme_dark_outlineVariant = Color(0xFF42474E)
+val md_theme_dark_outlineVariant = Color(0xFF55515B)
 val md_theme_dark_scrim = Color(0xFF000000)