Docs: update WCAG links and references (#40703)

Co-authored-by: Julien Déramond <juderamond@gmail.com>

scss/_functions.scss

@@ -177,7 +177,7 @@ $_luminance-list: .0008 .001 .0011 .0013 .0015 .0017 .002 .0022 .0025 .0027 .003
   @return if($l1 > $l2, divide($l1 + .05, $l2 + .05), divide($l2 + .05, $l1 + .05));
 }
 
-// Return WCAG2.1 relative luminance
+// Return WCAG2.2 relative luminance
 // See https://www.w3.org/TR/WCAG/#dfn-relative-luminance
 // See https://www.w3.org/TR/WCAG/#dfn-contrast-ratio
 @function luminance($color) {

scss/_variables.scss

@@ -67,8 +67,8 @@ $colors: (
 ) !default;
 // scss-docs-end colors-map
 
-// The contrast ratio to reach against white, to determine if color changes from "light" to "dark". Acceptable values for WCAG 2.0 are 3, 4.5 and 7.
-// See https://www.w3.org/TR/WCAG20/#visual-audio-contrast-contrast
+// The contrast ratio to reach against white, to determine if color changes from "light" to "dark". Acceptable values for WCAG 2.2 are 3, 4.5 and 7.
+// See https://www.w3.org/TR/WCAG/#contrast-minimum
 $min-contrast-ratio:   4.5 !default;
 
 // Customize the light and dark text colors for use in our color contrast function.

scss/mixins/_visually-hidden.scss

@@ -24,7 +24,7 @@
 // Use to only display content when it's focused, or one of its child elements is focused
 // (i.e. when focus is within the element/container that the class was applied to)
 //
-// Useful for "Skip to main content" links; see https://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G1
+// Useful for "Skip to main content" links; see https://www.w3.org/WAI/WCAG22/Techniques/general/G1.html
 
 @mixin visually-hidden-focusable() {
   &:not(:focus):not(:focus-within) {