Description

Handle @notify.close in the same manner as @check.close

CI has very infrequent failures. See https://github.com/puma/puma/runs/4085098935?check_suite_focus=true#step:9:385, which had the following error:

/Users/runner/work/puma/puma/lib/puma/server.rb:384:in `close': Bad file descriptor (Errno::EBADF)
	from /Users/runner/work/puma/puma/lib/puma/server.rb:384:in `handle_servers'
	from /Users/runner/work/puma/puma/lib/puma/server.rb:261:in `block in run'

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• I have added (or updated) appropriate tests if this PR fixes a bug or adds a feature.
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• All new and existing tests passed, including Rubocop.