#25221 run swift test

PR checklist

• Read the contribution guidelines.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

---

Summary by cubic

Adds SwiftPM test targets to the Swift 6 samples so generated client tests build and run in CI.

• Test targets are added to Package.swift in the default and combineLibrary samples with fixed test imports; UIKit-dependent code is guarded by #if canImport(UIKit) so tests compile on macOS.
• CI builds only the default sample on a macOS 15 Intel runner, starts Docker via Colima, runs a Petstore service container with an /etc/hosts entry, and runs the tests with xcodebuild on an iPhone 17 simulator; the other Swift 6 samples remain commented out.
• Documents running the tests in the sample README.md files.