platformtests: fix skipping encryption-only tests on systems that don't support encryption

(Or split the test into two tests  of which one is skipped depending on encryption support)

platformtest/tests/recvForceIntoEncryptedErr.go

@@ -10,6 +10,14 @@ import (
 )
 
 func ReceiveForceIntoEncryptedErr(ctx *platformtest.Context) {
+
+	supported, err := zfs.EncryptionCLISupported(ctx)
+	require.NoError(ctx, err, "encryption feature test failed")
+	if !supported {
+		ctx.SkipNow()
+		return
+	}
+
 	platformtest.Run(ctx, platformtest.PanicErr, ctx.RootDataset, `
 		DESTROYROOT
 		CREATEROOT