minor #5066 [Reference] enclose data type with double backticks (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
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[Reference] enclose data type with double backticks

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets |

Commits
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f5b9934 enclose data type with double backticks

reference/forms/types/options/data.rst.inc

@@ -1,7 +1,7 @@
 data
 ~~~~
 
-**type**: mixed **default**: Defaults to field of the underlying object (if there is one)
+**type**: ``mixed`` **default**: Defaults to field of the underlying object (if there is one)
 
 When you create a form, each field initially displays the value of the
 corresponding property of the form's domain object (if an object is bound