https://github.com/increments/mastodon/pull/125 お願いできた
increments/mastodonのローカルコピーで
$ git format-patch qiitadon
0001-Upgrade-excon-to-remove-DST-Root-CA-X3-from-its-cert.patch
0002-Remove-DST-Root-CA-X3-from-system-certificate-store.patch
してできたファイルをzunda/mastodonのローカルコピーに持ってきて
$ git remote add increments https://github.com/increments/mastodon.git
$ git fetch increments
$ git checkout -t increments/qiitadon
$ git switch -c increments/qiitadon-remove-dst-root-ca-x3
$ git am < 0001-Upgrade-excon-to-remove-DST-Root-CA-X3-from-its-cert.patch
$ git am < 0002-Remove-DST-Root-CA-X3-from-system-certificate-store.patch
$ git push -u origin increments/qiitadon-remove-dst-root-ca-x3
GitHubRemove DST Root CA x3 by zunda · Pull Request #125 · increments/mastodonRemove the expired root CA certificate from the system and excon's certificate stores to make it possible for the app code to verify certificates from remote servers provided by Let's Encrypt.