bug #56827 Fix CharsetValidator with string encoding (alamirault)

This PR was merged into the 7.1 branch.

Discussion
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Fix CharsetValidator with string encoding

| Q             | A
| ------------- | ---
| Branch?       | 7.1
| Bug fix?      | yes
| New feature?  | no <!-- please update src/**/CHANGELOG.md files -->
| Deprecations? | no <!-- please update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Issues        | Fix #56805 <!-- prefix each issue number with "Fix #", no need to create an issue if none exists, explain below instead -->
| License       | MIT

Commits
-------

f73afb9 Fix CharsetValidator with string encoding

src/Symfony/Component/Validator/Constraints/CharsetValidator.php

@@ -38,7 +38,7 @@ public function validate(mixed $value, Constraint $constraint): void
         if (!\in_array(mb_detect_encoding($value, $constraint->encodings, true), (array) $constraint->encodings, true)) {
             $this->context->buildViolation($constraint->message)
                 ->setParameter('{{ detected }}', mb_detect_encoding($value, strict: true))
-                ->setParameter('{{ encodings }}', implode(', ', $constraint->encodings))
+                ->setParameter('{{ encodings }}', implode(', ', (array) $constraint->encodings))
                 ->setCode(Charset::BAD_ENCODING_ERROR)
                 ->addViolation();
         }

src/Symfony/Component/Validator/Tests/Constraints/CharsetValidatorTest.php

@@ -37,13 +37,13 @@ public function testEncodingIsValid(string|\Stringable $value, array|string $enc
     /**
      * @dataProvider provideInvalidValues
      */
-    public function testInvalidValues(string $value, array $encodings)
+    public function testInvalidValues(string $value, array|string $encodings)
     {
         $this->validator->validate($value, new Charset(encodings: $encodings));
 
         $this->buildViolation('The detected character encoding is invalid ({{ detected }}). Allowed encodings are {{ encodings }}.')
             ->setParameter('{{ detected }}', 'UTF-8')
-            ->setParameter('{{ encodings }}', implode(', ', $encodings))
+            ->setParameter('{{ encodings }}', implode(', ', (array) $encodings))
             ->setCode(Charset::BAD_ENCODING_ERROR)
             ->assertRaised();
     }
@@ -73,6 +73,7 @@ public static function provideValidValues()
 
     public static function provideInvalidValues()
     {
+        yield ['my non-Äscîi string', 'ASCII'];
         yield ['my non-Äscîi string', ['ASCII']];
         yield ['😊', ['7bit']];
     }