minor #7009 Update form_dependencies.rst: fix DI (ReDnAxE)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #7009).

Discussion
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Update form_dependencies.rst: fix DI

Fix service definitions for `__construct(EntityManager $em)` argument

Commits
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7dbcb7c Update form_dependencies.rst: fix DI

Author: xabbuh

form/form_dependencies.rst

@@ -100,6 +100,7 @@ Next, register this as a service and tag it with ``form.type``:
         services:
             app.form.type.task:
                 class: AppBundle\Form\TaskType
+                arguments: ['@doctrine.orm.entity_manager']
                 tags:
                     - { name: form.type, alias: app_task }
 
@@ -113,6 +114,7 @@ Next, register this as a service and tag it with ``form.type``:
 
             <services>
                 <service id="app.form.type.task" class="AppBundle\Form\TaskType">
+                    <argument type="service" id="doctrine.orm.entity_manager"/>
                     <tag name="form.type" alias="app_task" />
                 </service>
             </services>
@@ -126,6 +128,7 @@ Next, register this as a service and tag it with ``form.type``:
                 'app.form.type.task',
                 'AppBundle\Form\TaskType'
             )
+            ->addArgument('@doctrine.orm.entity_manager')
             ->addTag('form.type', array(
                 'alias' => 'app_task',
             ))