Add workflow to auto-create PR on upstream Misskey release

[Copilot]

What

Adds .github/workflows/upstream-release-sync.yml — a scheduled GitHub Actions workflow that watches misskey-dev/misskey for new releases and automatically opens a PR to merge the upstream tag into develop.

Flow:

• Runs hourly (+ workflow_dispatch)
• Fetches the latest release tag from misskey-dev/misskey
• Checks for an existing upstream/<tag> branch — exits early if found (idempotent)
• Fetches the tag from upstream, creates and pushes upstream/<tag> branch
• Opens a PR against develop with the upstream release notes as the body; falls back to a plain description if notes are empty

Why

Upstream releases were tracked manually. Automating this ensures eveskey stays in sync with misskey-dev/misskey without human polling.

Additional info (optional)

The idempotency check uses git ls-remote on the branch name, so re-running the workflow against an already-synced release is a no-op. An explicit tag-existence check after git fetch surfaces clear error messages if the fetch silently fails.

Checklist

• Read the contribution guide
• Test working in a local environment
• (If needed) Update CHANGELOG.md
• (If possible) Add tests

Original prompt

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This section details on the original issue you should resolve

<issue_title>アップストリームでリリースが出たら自動でPRを作成するようにしたい</issue_title>
<issue_description>アップストリームでリリースが出たら自動でPRを作成するようにしたい。</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes アップストリームでリリースが出たら自動でPRを作成するようにしたい #2

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[Copilot]

Pull request overview

Adds an automated GitHub Actions workflow to keep this fork in sync with upstream Misskey releases by creating PRs that merge upstream release tags into develop.

Changes:

• Introduces a scheduled + manual-dispatch workflow to detect the latest upstream release tag.
• Creates/pushes an upstream/<tag> branch from the upstream tag (idempotent if branch already exists).
• Opens a PR to develop using upstream release notes as the PR body (with fallback text).

[techfish-11]

多分いいんじゃね知らんけど

[akku1139]

@copilot plz fix

[akku1139]

コンフリクト起きなかったらマージしてpushまでしちゃえば? (雑)

[akku1139]

改善案: (done)
gh pr list --head upstream/ブランチ でチェックして、
プルリクがマージされてからブランチが削除されても大丈夫にする

[akku1139]

もしかすると --state all をやめて、mergedに限定した方がいいかも

#3 (comment)

[akku1139]

良さそう

[akku1139]

.github/workflows/* に変更があった場合、権限不足で落ちる問題がある
これを解消するなら akku1139/viteplus-ja@6e7e6b7

1. ssh-keygen
2. Actions Secretの SYNC_PRIVATE_KEY に秘密鍵を置く
3. Deploy keysに公開鍵を登録
4. workflowでそれを使うようにする

もしくは、GitHub Appsを使う

(done)

[akku1139]

https://github.com/misskey-dev/misskey/commits/develop/.github/workflows

結構な頻度で更新されてるので、回避策が必要

[akku1139]

反応が無いのでマージしちゃう