ci: adjust python dependency update grouping (#81)

Even though the dashboard reports `pep621`, based on the docs and logs
that apparently only applies to `pdm.lock` and `uv.lock` files whereas
`poetry.lock` has its own category

Author: G-Rath

.github/renovate.json

@@ -12,7 +12,7 @@
       "pinDigests": true
     },
     {
-      "matchCategories": ["pep621"],
+      "matchCategories": ["poetry"],
       "groupName": "python"
     }
   ]