New age test vectors breaks age 1.2.1

Hi. The newly added `age` test vectors breaks self-tests of `age` version 1.2.1. Is that intentional? Do these two projects have to be updated in lock-step? That makes integrating them into distributions like Debian rather complicated, because we make independent releases of each Go project. We'll adapt of course, but understanding the situation helps, maybe this was just unintentional or part of some unfinished transition.

Self-test errors are here:

https://salsa.debian.org/jas/age/-/jobs/7077917

Compare a build of the exact same `age` packaging commit, but it uses an older version of C2SP-CCTV, that passes self-tests fine:

https://salsa.debian.org/jas/age/-/jobs/7074729

Some examples included below.

/Simon

```
--- PASS: TestVectors/stream_two_final_chunks_short (0.00s)
--- FAIL: TestVectors/stream_two_final_chunks_second (0.00s)
--- FAIL: TestVectors/stream_two_final_chunks_full (0.00s)
--- PASS: TestVectors/armor (0.01s)
--- FAIL: TestVectors/stream_two_chunks (0.00s)
--- FAIL: TestVectors/stream_trailing_garbage_short (0.00s)
--- FAIL: TestVectors/stream_trailing_garbage_long (0.00s)
--- FAIL: TestVectors/stream_three_chunks (0.00s)
--- FAIL: TestVectors/stream_short_second_chunk (0.00s)
--- PASS: TestVectors/stream_short_nonce (0.00s)
--- PASS: TestVectors/stream_short_chunk (0.00s)
--- PASS: TestVectors/stream_no_nonce (0.00s)
--- FAIL: TestVectors/stream_no_final_two_chunks_full (0.00s)
--- FAIL: TestVectors/stream_no_final_two_chunks (0.00s)
--- FAIL: TestVectors/stream_no_final_full (0.00s)
--- PASS: TestVectors/stream_no_final (0.00s)
--- PASS: TestVectors/stream_no_chunks (0.00s)
--- FAIL: TestVectors/stream_two_final_chunks (0.00s)
--- FAIL: TestVectors/stream_last_chunk_full_second (0.00s)
--- FAIL: TestVectors/stream_last_chunk_full (0.00s)
--- FAIL: TestVectors/stream_last_chunk_empty (0.00s)
--- PASS: TestVectors/stream_empty_payload (0.00s)
--- FAIL: TestVectors/stream_bad_tag_second_chunk_full (0.00s)
--- FAIL: TestVectors/stream_bad_tag_second_chunk (0.00s)
--- PASS: TestVectors/stream_bad_tag (0.00s)
--- FAIL: TestVectors/stream_258_chunks (0.00s)
--- FAIL: TestVectors/stream_257_chunks_full (0.00s)
--- FAIL: TestVectors/stream_257_chunks (0.00s)
--- PASS: TestVectors/stanza_valid_characters (0.00s)
```

Start with the linked Debian CI jobs and the failing TestVectors cases to compare the behavior with the older C2SP-CCTV version that passes. Trace which newly added vectors cause age 1.2.1 to fail and determine whether compatibility requires lock-step releases. Done means the compatibility relationship and any required change are clearly established.

Written by the indexing model from the issue text.