minor #12503 Fix code indentation (jerodev)

This PR was merged into the 4.3 branch.

Discussion
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Fix code indentation

Fix code indentation for `MessageFormat` documentation.

The code snipped used tabs instead of spaces which broke the indentation.

Commits
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be51b88 Fix code indentation

Author: javiereguiluz

translation/message_format.rst

@@ -239,7 +239,7 @@ Usage of this string is the same as with variables and select::
 
     .. code-block:: text
 
-		{gender_of_host, select,
+        {gender_of_host, select,
             female {
                 {num_guests, plural, offset:1
                 =0    {{host} does not give a party.}