Fix typo in variales.

Author: priveraussi

projects/material-css-vars/src/lib/_variables.scss

@@ -435,7 +435,7 @@ $mat-css-palette-warn-no-rgb: (
     600: var(--palette-warn-contrast-600-no-rgb),
     700: var(--palette-warn-contrast-700-no-rgb),
     800: var(--palette-warn-contrast-800-no-rgb),
-    900: var(--palette-warn-contrast-900b-no-rgb),
+    900: var(--palette-warn-contrast-900-no-rgb),
     A100: var(--palette-warn-contrast-A100-no-rgb),
     A200: var(--palette-warn-contrast-A200-no-rgb),
     A400: var(--palette-warn-contrast-A400-no-rgb),