Fix disposing root X.509 certificate prematurely for OCSP stapling (#82116)

Fix disposing root X.509 certificate prematurely for OCSP stapling (#82116)

In SslStreamCertificateContext, don't dispose of the root cert if it's about to be handed to the AddRootCert PAL call,
which was the high-level cause of a segfault when handling certificate chains of length 2 in OCSP Stapling on Linux.

This change additionally guards against disposed certificates in the OCSP Stapling retriever (disabling the feature
instead of segfaulting), and adds tests to ensure that we don't regress 2-cert chains in the future.