ci: Add some pytest marks and reporting.

[dougch]

Resolved issues:

none

Description of changes:

While sorting out the integration tests needing attention when running in a nix environment, we were looking for a way to track what's left. Using pytest's mark feature, simply as a reporting mechanism is helpful. This PR is intended to spark discussion about the use of marks.

Sample output

>nix develop
>pytestmark_report nix
+---------------------------------------------------------+
| Tests with the nix mark                                 |
+---------------------------------------------------------+
tests/integrationv2/test_buffered_send.py: 7651
tests/integrationv2/test_client_authentication.py: 1308
tests/integrationv2/test_early_data.py: 3964
tests/integrationv2/test_fragmentation.py: 72
tests/integrationv2/test_hello_retry_requests.py: 457
tests/integrationv2/test_key_update.py: 7
tests/integrationv2/test_npn.py: 1010
tests/integrationv2/test_ocsp.py: 576
tests/integrationv2/test_pq_handshake.py: 82
tests/integrationv2/test_record_padding.py: 126
tests/integrationv2/test_renegotiate.py: 1010
tests/integrationv2/test_session_resumption.py: 7412
tests/integrationv2/test_signature_algorithms.py: 6126
tests/integrationv2/test_sni_match.py: 88
tests/integrationv2/test_version_negotiation.py: 6673
tests/integrationv2/test_well_known_endpoints.py: 480

+---------------------------------------------------------+
| Tests without the nix mark                              |
+---------------------------------------------------------+
tests/integrationv2/test_cross_compatibility.py: 3336
tests/integrationv2/test_dynamic_record_sizes.py: 1278
tests/integrationv2/test_external_psk.py: 4159
tests/integrationv2/test_happy_path.py: 8552
tests/integrationv2/test_pq_handshake.py: 5
tests/integrationv2/test_record_padding.py: 127
tests/integrationv2/test_renegotiate_apache.py: 28
tests/integrationv2/test_signature_algorithms.py: 6126

Call-outs:

This changes nothing about how tests are currently run.

Testing:

How is this change tested (unit tests, fuzz tests, etc.)? locally

Is this a refactor change? If so, how have you proved that the intended behavior hasn't changed?

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.