minor #31629 Small grammar mistake in documentation (michaelKaefer)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes #31629).

Discussion
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Small grammar mistake in documentation

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Commits
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ec098d6 Small grammar mistake in documentation

src/Symfony/Component/HttpKernel/Controller/ControllerResolverInterface.php

@@ -31,7 +31,7 @@ interface ControllerResolverInterface
      * As several resolvers can exist for a single application, a resolver must
      * return false when it is not able to determine the controller.
      *
-     * The resolver must only throw an exception when it should be able to load
+     * The resolver must only throw an exception when it should be able to load a
      * controller but cannot because of some errors made by the developer.
      *
      * @return callable|false A PHP callable representing the Controller,