bug #62182 [VarDumper] Fix dumping CurlHttpClient instances (nicolas-grekas)

This PR was merged into the 7.4 branch.

Discussion
----------

[VarDumper] Fix dumping CurlHttpClient instances

| Q             | A
| ------------- | ---
| Branch?       | 7.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | -
| License       | MIT

Too niche for a test case 🙏 😬

Commits
-------

d8f05d45d45 [VarDumper] Fix dumping CurlHttpClient instances

Author: nicolas-grekas

Caster/SymfonyCaster.php

@@ -51,7 +51,7 @@ public static function castRequest(Request $request, array $a, Stub $stub, bool
     public static function castHttpClient($client, array $a, Stub $stub, bool $isNested): array
     {
         $multiKey = \sprintf("\0%s\0multi", $client::class);
-        if (isset($a[$multiKey])) {
+        if (isset($a[$multiKey]) && !$a[$multiKey] instanceof Stub) {
             $a[$multiKey] = new CutStub($a[$multiKey]);
         }