chore: prevent future issues when min stability is set

Author: SychO9

extensions/package-manager/src/Api/Controller/ConfigureComposerController.php

@@ -95,6 +95,9 @@ protected function composerConfig(ServerRequestInterface $request): array
                 Arr::set($composerJson, $key, $value);
             }
 
+            // Always prefer stable releases.
+            $composerJson['prefer-stable'] = true;
+
             $this->composerJson->set($composerJson);
         }