minor #6344 Altered single / multiple inheritance sentence (outspaced)

This PR was submitted for the 3.0 branch but it was merged into the 2.3 branch instead (closes #6344).

Discussion
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Altered single / multiple inheritance sentence

The way the sentence was didn't really make sense, and was difficult to process

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

Commits
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a34fb2e Altered single / multiple inheritance sentence

Author: xabbuh

components/event_dispatcher/introduction.rst

@@ -22,8 +22,8 @@ answer.
 Consider the real-world example where you want to provide a plugin system
 for your project. A plugin should be able to add methods, or do something
 before or after a method is executed, without interfering with other plugins.
-This is not an easy problem to solve with single and multiple inheritance
-(were it possible with PHP) has its own drawbacks.
+This is not an easy problem to solve with single inheritance, and even if 
+multiple inheritance was possible with PHP, it comes with its own drawbacks.
 
 The Symfony EventDispatcher component implements the `Mediator`_ pattern
 in a simple and effective way to make all these things possible and to make