test(config): assert DD_APPSEC_AGENTIC_ONBOARDING in v5 appsec config (#9489)

The v5-only "should give priority to non-experimental options" test does a
strict deepStrictEqual on config.appsec. PR #9486 added
DD_APPSEC_AGENTIC_ONBOARDING as a namespace:"appsec" entry (default ""),
which populates config.appsec for all majors, but that test was gated on
DD_MAJOR < 6 and therefore skipped in master (v6/v7) CI. It only runs in
the v5 release pipeline, where the missing key broke the assertion.

Add the always-present key to the expected object.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 2 people

packages/dd-trace/test/config/index.spec.js

@@ -2804,6 +2804,7 @@ describe('Config', () => {
       },
       rateLimit: 42,
       rules: RULES_JSON_PATH,
+      DD_APPSEC_AGENTIC_ONBOARDING: '',
       DD_APPSEC_SCA_ENABLED: undefined,
       stackTrace: {
         enabled: true,