`ProviderArgsEncoder` does not preserve "secretness"

[pawelprazak]

This test fails:

test("encode secret ProviderArgs".ignore) {
    given Context = DummyContext().unsafeRunSync()
    val pae       = summon[ProviderArgsEncoder[ProviderArgs]]

    val args         = ProviderArgs(kubeconfig = Output.secret("abcd"))
    val (_, encoded) = pae.encode(args, _ => false).unsafeRunSync()

    val expected = Map("kubeconfig" -> "abcd".asValue.asSecret).asValue

    assertNoDiff(pprint(encoded.asValue).plainText, pprint(expected).plainText)
    assertEqualsValue(encoded.asValue, expected)
  }

The secret was not preserved.

[pawelprazak]

fixed by #414