minor #4278 Missing word in DependencyInjection => Types of Injection (fabschurt)

This PR was merged into the 2.3 branch.

Discussion
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Missing word in DependencyInjection => Types of Injection

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3+
| Fixed tickets | n/a

Commits
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2377280 Insert a missing word

Author: wouterj

components/dependency_injection/types.rst

@@ -170,8 +170,8 @@ The disadvantages of setter injection are:
 
 * The setter can be called more than just at the time of construction so
   you cannot be sure the dependency is not replaced during the lifetime of the
-  object (except by explicitly writing the setter method to check if has already been
-  called).
+  object (except by explicitly writing the setter method to check if it has already
+  been called).
 
 * You cannot be sure the setter will be called and so you need to add checks
   that any required dependencies are injected.