test cases fail on RHEL9 due to SHA1 deprecation

[ktdreyer]

CentOS 9 Stream and Red Hat Enterprise Linux 9 have SHA-1 signatures disabled by default.

A couple unit tests fail on RHEL 9:

ERROR tests/test_10_exceptions.py::TestPGPKey::test_add_key_with_subkeys_as_subkey
FAILED tests/test_05_actions.py::TestPGPKey_Actions::test_verify_invalid_sig[pkspec0]
FAILED tests/test_99_regressions.py::test_spurious_dash_escapes - cryptograph...

The error is:

cryptography.exceptions.UnsupportedAlgorithm: sha1 is not supported by this backend for RSA signing.