bug symfony#12954 Fix Typo (belghiti)

This PR was submitted for the 4.4 branch but it was merged into the 3.4 branch instead (closes symfony#12954).

Discussion
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Fix Typo

Fix a typo in line 12 is build => is built

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Commits
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ef087ab Fix Typo

Author: OskarStark

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

@@ -9,7 +9,7 @@ option was not set. This is useful when using
 
 If you're using keyword translation messages as labels, you often end up having
 multiple keyword messages for the same label (e.g. ``profile_address_street``,
-``invoice_address_street``). This is because the label is build for each "path"
+``invoice_address_street``). This is because the label is built for each "path"
 to a field. To avoid duplicated keyword messages, you can configure the label
 format to a static value, like::