feat(electron-publish): add targetCommitish support for GitHub releases

[EYadroshnikov]

feat(electron-publish): add targetCommitish support for GitHub releases

Summary

Adds support for specifying which branch or commit GitHub releases are created from. By default, GitHub uses the default branch (e.g. main); this change allows targeting a specific branch (e.g. development) or a commit SHA.

Motivation

Useful when:

• Releasing from non-default branches (e.g. development, release/1.0)
• Creating releases from the exact commit built in CI (e.g. GITHUB_SHA in GitHub Actions)

Changes

• GithubOptions (builder-util-runtime): Added optional targetCommitish field
• GitHubPublisher (electron-publish): Resolves targetCommitish from config, EP_TARGET_COMMITISH, or GITHUB_SHA env vars and passes it as target_commitish in the GitHub API request
• Schema (app-builder-lib/scheme.json): Added targetCommitish property
• Documentation (pages/publish.md): Added usage examples and env var notes
• Tests: New GitHubPublisherTest.ts covering config, env vars, and precedence

Usage

Config:

{
  "build": {
    "publish": {
      "provider": "github",
      "owner": "my-org",
      "repo": "my-app",
      "targetCommitish": "development"
    }
  }
}

[changeset-bot]

🦋 Changeset detected

Latest commit: b192372

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
electron-publish	Major
builder-util-runtime	Minor
app-builder-lib	Major
builder-util	Major
electron-builder	Major
electron-updater	Patch
dmg-builder	Major
electron-builder-squirrel-windows	Major
electron-forge-maker-appimage	Major
electron-forge-maker-nsis-web	Major
electron-forge-maker-nsis	Major
electron-forge-maker-snap	Major

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[EYadroshnikov]

@mmaietta, this is ready for review whenever you have some time. Thanks!

[mmaietta]

Thanks for adding docs/example! I left a comment re: this being a breaking change since we're adding conditional functionality that impacts prod tagging based on environment variables.
In order to proceed with this PR, I'd advocate for reading only from the config property and then allow it to be opt-in for v26.

Happy to discuss making it the default logic for v27 though!

[mmaietta]

I'm hesitant to add the default of process.env.EP_TARGET_COMMITISH ?? process.env.GITHUB_SHA since this is completely net-new functionality and likely not expected by another dev.
I consider new functionality that is extracted from env vars to be breaking changes.

I'd suggest only using info.targetCommitish and then in the tsdoc, specify an example (or recommended) value.

[mmaietta]

Nit: We can simplify this to !!this.targetCommitish?.length (or use isEmptyOrSpaces from builder-util)