test: fix test/parallel/test-tls-server-verify.js on Windows CI
The test runs two test cases at a time. This is not relevant to what the test is actually testing. Not sure why doing it that way causes a deadlock on some Windows servers, but running one at a time fixes it.
Fixes: https://github.com/nodejs/node/issues/18269
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
test