GitHub でこのノートブックを閲覧する権限があることを確認し、Colab に GitHub API の使用を許可してください。
Fetch for https://api.github.com/repos/flutter/codelabs/contents/tfrs-flutter/step1/backend/ranking?per_page=100&ref=master failed: {"message":"No commit found for the ref master","documentation_url":"https://docs.github.com/v3/repos/contents/","status":"404"} CustomError: Fetch for https://api.github.com/repos/flutter/codelabs/contents/tfrs-flutter/step1/backend/ranking?per_page=100&ref=master failed: {"message":"No commit found for the ref master","documentation_url":"https://docs.github.com/v3/repos/contents/","status":"404"} at new jN (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:2500:68) at wa.program_ (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:2483:436) at za (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:16:57) at wa.next_ (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:14:195) at kaa.next (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:17:48) at b (https://ssl.gstatic.com/colaboratory-static/common/629c0c0894a411e1c2ceca4f346d8829/external_binary_l10n__ja.js:17:309)