[CI] test_integration_ssl_session.rb - wait for session callback

[MSP-Greg]

Description

I haven't seen any of these tests fail, but I have seen some retry. All of the tests create two ssl requests, and the SSLSockets have OpenSSL::SSL::SSLContext#session_new_cb set.

This PR adds code so the second request waits for the callback. The tests haven't failed/retried in the limited CI testing I've done.

Note that, like many of the tests involving 'retry', I've never had these tests fail locally.

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