fix: prevent handle leak in default e2e test

[OSA413]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior?

After the test is run, jest will hang telling

Jest did not exit one second after the test run has completed.

This usually means that there are asynchronous operations that weren't stopped in your tests. Consider running Jest with `--detectOpenHandles` to troubleshoot this issue.

What is the new behavior?

It closes the app so the Jest can exit.

Does this PR introduce a breaking change?

• Yes
• No

[coveralls]

Pull Request Test Coverage Report for Build 9d64d54d-aa97-4252-b895-835046dc5af2

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.044%

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Totals
Change from base Build 5cf0e473-a21f-4756-8d9d-72a40ee32710:	0.0%
Covered Lines:	5763
Relevant Lines:	6128

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💛 - Coveralls