Please skip CI jobs that run on self-hosted runners on forked repositories

[kkebo]

The following jobs run on self-hosted runners.

• github-workflows/.github/workflows/swift_package_test.yml

  Line 289 in 497d9ab

  runs-on: [self-hosted, macos, "${{ matrix.os_version }}", "${{ matrix.arch }}"]

• github-workflows/.github/workflows/swift_package_test.yml

  Line 331 in 497d9ab

  runs-on: [self-hosted, macos, "${{ matrix.os_version }}", "${{ matrix.arch }}"]

• github-workflows/.github/workflows/swift_package_test.yml

  Line 378 in 497d9ab

  runs-on: [self-hosted, macos, "${{ matrix.os_version }}", "${{ matrix.arch }}"]

However, the self-hosted runner is not available for forked repositories. This causes CI to hang and fail after a long period of time on forked repositories. This is really annoying for contributors.

Example:

• https://github.com/kkebo/swift-format/actions/runs/29786351877/job/88498627076?pr=872
  • This job was invoked from https://github.com/swiftlang/swift-format/blob/7ddf4e1e322f3aae00a338720d82485ab9e4fc94/.github/workflows/pull_request.yml#L27.

Similar cases from the past:

• Skip macOS CI jobs on forked repositories swiftly#471