Make setRequestDowngrade @TestApi

Test: build
Bug: 134653708
Change-Id: Idf99e0810e2e9040f49f06a00722567ac15bbe18
diff --git a/api/test-current.txt b/api/test-current.txt
index 14c70e3..cfb6435 100644
--- a/api/test-current.txt
+++ b/api/test-current.txt
@@ -696,6 +696,7 @@
     method public void setEnableRollback(boolean);
     method @RequiresPermission("android.permission.INSTALL_GRANT_RUNTIME_PERMISSIONS") public void setGrantedRuntimePermissions(String[]);
     method @RequiresPermission(android.Manifest.permission.INSTALL_PACKAGES) public void setInstallAsApex();
+    method public void setRequestDowngrade(boolean);
     method @RequiresPermission(android.Manifest.permission.INSTALL_PACKAGES) public void setStaged();
   }
 
diff --git a/core/java/android/content/pm/PackageInstaller.java b/core/java/android/content/pm/PackageInstaller.java
index 3cecd7f..1099d8b 100644
--- a/core/java/android/content/pm/PackageInstaller.java
+++ b/core/java/android/content/pm/PackageInstaller.java
@@ -1565,7 +1565,7 @@
         }
 
         /** {@hide} */
-        @SystemApi
+        @SystemApi @TestApi
         public void setRequestDowngrade(boolean requestDowngrade) {
             if (requestDowngrade) {
                 installFlags |= PackageManager.INSTALL_REQUEST_DOWNGRADE;