Fix typos in two examples (act-rules#2057)

* Fix typos in two examples

* Update _rules/aria-required-context-role-ff89c9.md

Author: WilcoFiers

_rules/aria-required-context-role-ff89c9.md

@@ -222,10 +222,10 @@ This `section` element with an [explicit role][] of `doc-abstract` has a role fr
 
 #### Inapplicable Example 4
 
-There is no element whose role has [required context role][] because the `header` role does not have one.
+There is no element whose role has [required context role][] because the `heading` role does not have one.
 
 ```html
-<div role="header" aria-level="1">Hello!</div>
+<div role="heading" aria-level="1">Hello!</div>
 <p>Welcome to my homepage!</p>
 ```
 

_rules/text-contrast-afw4f7.md

@@ -346,7 +346,7 @@ This text not part of a [text node][].
 
 ```html
 <p>
-	<img scr="/test-assets/contrast/example.png" alt="example" />
+	<img src="/test-assets/contrast/example.png" alt="example" />
 </p>
 ```