[ci] setup-swift is too flaky

[prabhu]

/usr/bin/gpg --import /home/runner/work/_temp/d8b77b08-5628-483c-aae0-6084db31ca77
gpg: directory '/home/runner/.gnupg' created
gpg: keybox '/home/runner/.gnupg/pubring.kbx' created
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0
Error: Unexpected error, unable to continue. Please report at https://github.com/swift-actions/setup-swift/issues
The process '/usr/bin/gpg' failed with exit code 2
Stacktrace:
Error: The process '/usr/bin/gpg' failed with exit code 2
    at ExecState._setResult (/home/runner/work/_actions/swift-actions/setup-swift/v2/dist/index.js:3190:25)

swift-actions/setup-swift#592
swiftlang/swift#68047

We need to separate the particular test into a job and run it with the swift container image.