fix(provider): normalize baseUrl before assigning readonly property

Promoted readonly properties can't be reassigned in the constructor
body, so GitLabProvider and GiteaProvider threw on every instantiation.
Normalize the plain parameter first, then assign to a separately
declared readonly property.

src/Service/Provider/GitLabProvider.php

@@ -19,14 +19,16 @@ final class GitLabProvider implements ProviderInterface
 {
     use ProbeTrait;
 
+    private readonly string $baseUrl;
+
     public function __construct(
         private readonly HttpClientInterface $client,
         private readonly string $username,
         private readonly string $token,
         private readonly LoggerInterface $logger,
-        private readonly string $baseUrl = '',
+        string $baseUrl = '',
     ) {
-        $this->baseUrl = rtrim($this->baseUrl !== '' ? $this->baseUrl : 'https://gitlab.com', '/');
+        $this->baseUrl = rtrim($baseUrl !== '' ? $baseUrl : 'https://gitlab.com', '/');
     }
 
     public function getName(): string