gh-116333: Relax error string text expectations in SSL-related tests (GH-116334)

gh-116333: Relax error string text expectations in SSL-related tests (GH-116334)

* Relax error string text expectations in SSL-related tests

As suggested [here][1], this change relaxes the OpenSSL error string
text expectations in a number of tests. This was specifically done in
support of more easily building CPython [AWS-LC][2], but because AWS-LC
is a fork of [BoringSSL][3], it should increase compatibility with that
library as well.

In addition to the error string relaxations, we also add some guards
around the `tls-unique` channel binding being used with TLSv1.3, as that
feature (described in [RFC 6929][4]) is [not defined][5] for TLSv1.3.

[1]: https://discuss.python.org/t/support-building-ssl-and-hashlib-modules-against-aws-lc/44505/4
[2]: https://github.com/aws/aws-lc
[3]: https://github.com/google/boringssl
[4]: https://datatracker.ietf.org/doc/html/rfc5929#section-3
[5]: https://datatracker.ietf.org/doc/html/rfc8446#appendix-C.5