Commit Message: the test failed after #32260 because the test server uses a mocked MockTransportSocketFactoryContext which doesn't return a real ContextManager object in sslContextManager(). The mocked object returns nullptr in createSslServerContext(), thus fail to initialize the new member ssl_ctx_ in QuicServerTransportSocketFactory.

Additional Description: bazel test //test/java/io/envoyproxy/envoymobile/engine/testing:quic_test_server_test passes in this PR
Risk Level: low, test only
Testing: existing tests pass
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

Request variables

Key	Value
ref	685aa436ae51b40cd353bcf694482ce157a153ad
sha	b668a2d
pr	32755
base-sha	a19dce3
actor	@danzh2010
message	mobile: fix quic_test_server_test...
started	1709768386.79198
target-branch	main
trusted	false

Container image/s (as used in this CI run)

Envoy version (as used in this CI run)