fix(websockets): ensure non-shared servers call close method

[sapenlei]

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?

When forceCloseConnections is enabled, non-shared HTTP servers are not being properly closed.

What is the new behavior?

When forceCloseConnections is enabled, non-shared HTTP servers should be closed by WS.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[coveralls]

Pull Request Test Coverage Report for Build 4c4cc718-726a-4220-b5c9-b60fa58e9ff1

Details

• 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 91.944%

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Totals
Change from base Build f8530e24-4ee6-4945-a04b-213174f935d6:	0.0%
Covered Lines:	6814
Relevant Lines:	7411

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💛 - Coveralls

[kamilmysliwiec]

LGTM