minor symfony#24002 Fix case sensitive typo in use class name (PhilETaylor)

This PR was merged into the 3.3 branch.

Discussion
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Fix case sensitive typo in use class name

closes symfony#24001

Change is simple typo: Parameterbag = ParameterBag

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

Fixes this:

`
  [RuntimeException]
  An error occurred when executing the "'cache:clear --no-warmup'" command:
  Fatal error: Uncaught RuntimeException: Case mismatch between loaded and declared class names: "Symfony\Component\DependencyInjection\Parameterbag\EnvPlaceholderParameterBag" v
  s "Symfony\Component\DependencyInjection\ParameterBag\EnvPlaceholderParameterBag". in /Users/phil/Sites/maintain.myjoomla.com/vendor/symfony/symfony/src/Symfony/Component/Debug
  /DebugClassLoader.php:165
`

Commits
-------

6fe9072 Fix case sensitive typo in use class name

Author: fabpot

src/Symfony/Component/DependencyInjection/Compiler/MergeExtensionConfigurationPass.php

@@ -15,7 +15,7 @@
 use Symfony\Component\DependencyInjection\Extension\ConfigurationExtensionInterface;
 use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Extension\PrependExtensionInterface;
-use Symfony\Component\DependencyInjection\Parameterbag\EnvPlaceholderParameterBag;
+use Symfony\Component\DependencyInjection\ParameterBag\EnvPlaceholderParameterBag;
 
 /**
  * Merges extension configs into the container builder.