Require NSS 3.69+ due to issues with SQLite
When building certmonger with NSS < 3.69, tests hang indefinitely at the 002-keygen-rsa test. This is due to a bug in NSS and its interaction with newer versions of SQLite (3.34.0+), which is described in https://pagure.io/certmonger/issue/188.
This requires at least NSS 3.69, preventing accidental builds with a faulty version of NSS.