Fix CI failures

[traversaro]

Post merge of #99, see https://github.com/RoboStack/vinca/actions/runs/18952398882/job/54120213104 :

✨ Pixi task (lint-check): ruff check .
invalid-syntax: Cannot use named assignment expression (`:=`) on Python 3.7 (syntax was added in Python 3.8)
    --> vinca/main.py:1029:8
     |
1027 |     }
1028 |
1029 |     if test := vinca_conf.get("_tests", {}).get(final_name):
     |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
1030 |         # parse as yaml
1031 |         text = test.read_text()
     |

invalid-syntax: Cannot use named assignment expression (`:=`) on Python 3.7 (syntax was added in Python 3.8)
   --> vinca/template.py:122:16
    |
120 |             meta["build"]["post_process"] = post_process_items
121 |
122 |             if test := vinca_conf["_tests"].get(o["package"]["name"]):
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
123 |                 print("Using test: ", test)
124 |                 text = test.read_text()
    |

Found 2 errors.