Fix flaky doubleEndMethodOnVercel test

[AbhiPrasad]

Problem Statement

The doubleEndMethodOnVercel test in the NextJS integration tests are flaky. See an example here: https://github.com/getsentry/sentry-javascript/actions/runs/3930047407/jobs/6719941317

This test was introduced here: #6674

[nextjs@10 | webpack@5] Running server tests with options: --silent
X Scenario failed: doubleEndMethodOnVercel.js (line: 9)
'' == '{"success":true}'
✓ Scenario succeded: errorApiEndpoint.js
✓ Scenario succeded: errorServerSideProps.js
✓ Scenario succeded: excludedApiEndpoints.js
✓ Scenario succeded: tracing200.js
✓ Scenario succeded: tracing500.js
✓ Scenario succeded: tracingServerGetInitialProps.js
✓ Scenario succeded: tracingServerGetServerSideProps.js
✓ Scenario succeded: tracingServerGetServerSidePropsCustomPageExtension.js
✓ Scenario succeded: tracingWithSentryAPI.js
✓ Scenario succeded: tracingHttp.js
✓ Scenario succeded: cjsApiEndpoints.js
X Some scenarios failed
[nextjs@10 | webpack@5] Server integration tests failed
[nextjs] Cleaning up...
[nextjs] Test run complete
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
Error: Process completed with exit code 1.

Solution Brainstorm

This might be indicative of a deeper issue here, that the fix in #6674 did not work. As such, it might require some more investigation into alternative wrapping strategies for res.end.