[release-branch.go1.12] crypto/x509: fix value ownership in isSSLPolicy on macOS
    
    CFDictionaryGetValueIfPresent does not take ownership of the value, so
    releasing the properties dictionary before passing the value to CFEqual
    can crash. Not really clear why this works most of the time.
    
    See https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html
    
    Fixes #32282
    Updates #28092
    Updates #30763
    
    Change-Id: I5ee7ca276b753a48abc3aedfb78b8af68b448dd4
    Reviewed-on: https://go-review.googlesource.com/c/go/+/178537
    Reviewed-by: Adam Langley <agl@golang.org>
    (cherry picked from commit a3d4655c2435e3777c45f09650539b943bab1c66)
    Reviewed-on: https://go-review.googlesource.com/c/go/+/179339
    Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>