⬆️(docker) upgrade backend image to python 3.13

Python 3.13 is now stable, our libraries are compatible with it. We also
upgrade the alpine version used in order to fix CVE related to libxml2

src/backend/core/tests/documents/test_api_documents_attachment_upload.py

@@ -410,5 +410,9 @@ def test_api_documents_attachment_upload_unsafe():
         "is_unsafe": "true",
         "status": "processing",
     }
-    assert file_head["ContentType"] == "application/octet-stream"
+    # Depending the libmagic version, the content type may change.
+    assert file_head["ContentType"] in [
+        "application/x-dosexec",
+        "application/octet-stream",
+    ]
     assert file_head["ContentDisposition"] == 'attachment; filename="script.exe"'