Added text-shadow failure - Text has minimum contrast [afw4f7] (#2184)

* Added text-shadow failed example

* Update _rules/text-contrast-afw4f7.md

Co-authored-by: Wilco Fiers <WilcoFiers@users.noreply.github.com>

* Update text-contrast-afw4f7.md

* Update text-contrast-afw4f7.md

* Update spelling-ignore.yml

---------

Co-authored-by: Wilco Fiers <WilcoFiers@users.noreply.github.com>
Co-authored-by: Carlos Duarte <carlosapaduarte@gmail.com>
Co-authored-by: Jean-Yves Moyen <jym@siteimprove.com>

Author: 4 people

__tests__/spelling-ignore.yml

@@ -239,6 +239,7 @@
 - unitless
 - luminance
 - disambiguated
+- grey
 
 # Parts of Unicode
 - 000A

_rules/text-contrast-afw4f7.md

@@ -296,6 +296,16 @@ This text in a [semantic button][semantic role] has a contrast ratio of 3.85:1.
 <div role="button" style="color: #777; background: #EEE;">My button!</div>
 ```
 
+#### Failed Example 11
+
+The grey text has a contrast between 2.7:1 and 2.9:1 against the grey text shadow.
+
+```html
+<p style="background: #fff; color: #666; text-shadow: #aaa 2px 2px 4px, #aaa -2px 2px 4px, #aaa 2px -2px 4px, #aaa -2px -2px 4px;">
+    Some text in a human language
+  </p>
+```
+
 ### Inapplicable
 
 #### Inapplicable Example 1