minor #9805 Update NotBlank constraint description (sidux)

This PR was submitted for the 4.0 branch but it was merged into the 2.7 branch instead (closes #9805).

Discussion
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Update NotBlank constraint description

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Include `false` in validator NotBlank constraint description

Commits
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d059bee Update NotBlank constraint description

Author: javiereguiluz

reference/constraints/NotBlank.rst

@@ -2,7 +2,7 @@ NotBlank
 ========
 
 Validates that a value is not blank - meaning not equal to a blank string,
-a blank array or ``null``::
+a blank array, ``null`` or ``false``::
 
     if (false === $value || (empty($value) && '0' != $value)) {
         // validation will fail