Fix incorrect test assertion for string input in Anthropic no-truncation scenario

messagesFromParams wraps string input values into an array, so the
expected attribute value is JSON.stringify([longStringInput]), not the
raw string.

Author: andreiborza

dev-packages/node-integration-tests/suites/tracing/anthropic/scenario-no-truncation.mjs

@@ -37,7 +37,7 @@ async function run() {
       messages: [{ role: 'user', content: longContent }],
     });
 
-    // Long string input (should not be wrapped in quotes)
+    // Long string input (messagesFromParams wraps it in an array)
     const longStringInput = 'B'.repeat(50_000);
     await client.messages.create({
       model: 'claude-3-haiku-20240307',

dev-packages/node-integration-tests/suites/tracing/anthropic/test.ts

@@ -816,10 +816,10 @@ describe('Anthropic integration', () => {
           [GEN_AI_INPUT_MESSAGES_ORIGINAL_LENGTH_ATTRIBUTE]: 1,
         }),
       }),
-      // Long string input should not be truncated or wrapped in quotes
+      // Long string input should not be truncated (messagesFromParams wraps it in an array)
       expect.objectContaining({
         data: expect.objectContaining({
-          [GEN_AI_INPUT_MESSAGES_ATTRIBUTE]: longStringInput,
+          [GEN_AI_INPUT_MESSAGES_ATTRIBUTE]: JSON.stringify([longStringInput]),
           [GEN_AI_INPUT_MESSAGES_ORIGINAL_LENGTH_ATTRIBUTE]: 1,
         }),
       }),