test(core): Init client in integration attribute tests so _integrations is populated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: nicohrubec

packages/core/test/lib/tracing/spans/captureSpan.test.ts

@@ -250,6 +250,7 @@ describe('captureSpan', () => {
         },
       }),
     );
+    client.init();
 
     const span = withScope(scope => {
       scope.setClient(client);
@@ -297,6 +298,7 @@ describe('captureSpan', () => {
         integrations: [{ name: 'InboundFilters', setupOnce: () => {} }],
       }),
     );
+    client.init();
 
     const serializedChild = withScope(scope => {
       scope.setClient(client);