Move some VM config APIs to @TestApi

Another change in this topic allows java_sdk_libraries belonging to
non-updatable APEXes to contribute to test API stubs.

Since  getPayloadConfigPath() and setPayloadConfigPath() are not
expected to be part of the @SystemApi, move them to @TestApi.

Bug: 261004711
Test: presubmit
Change-Id: I48a19ed925cc0c75cf6a965699aaa291508ea7d7
diff --git a/javalib/api/test-current.txt b/javalib/api/test-current.txt
index d802177..42ad060 100644
--- a/javalib/api/test-current.txt
+++ b/javalib/api/test-current.txt
@@ -1 +1,13 @@
 // Signature format: 2.0
+package android.system.virtualmachine {
+
+  public final class VirtualMachineConfig {
+    method @Nullable public String getPayloadConfigPath();
+  }
+
+  public static final class VirtualMachineConfig.Builder {
+    method @NonNull @RequiresPermission(android.system.virtualmachine.VirtualMachine.USE_CUSTOM_VIRTUAL_MACHINE_PERMISSION) public android.system.virtualmachine.VirtualMachineConfig.Builder setPayloadConfigPath(@NonNull String);
+  }
+
+}
+