Removed extra 't' in targetting (#4324)

.github/PULL_REQUEST_TEMPLATE.md

@@ -7,7 +7,7 @@
     - master is for deprecation removals and other changes that cannot be done without a BC-break
     More details here: https://github.com/sonata-project/SonataAdminBundle/blob/3.x/CONTRIBUTING.md#the-base-branch
 -->
-I am targetting this branch, because {reason}.
+I am targeting this branch, because {reason}.
 
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