Add missing header.

Protobuf 22.x no longer includes <unordered_map>, so it has to
be included explicitly.

Bug: 329747255
Test: presubmit
Change-Id: Icd5055e242e4f58029caf80cbb321222c612a9d0
diff --git a/init/persistent_properties.cpp b/init/persistent_properties.cpp
index 6f8a4de..59e57b9 100644
--- a/init/persistent_properties.cpp
+++ b/init/persistent_properties.cpp
@@ -23,6 +23,7 @@
 #include <sys/types.h>
 
 #include <memory>
+#include <unordered_map>
 
 #include <android-base/file.h>
 #include <android-base/logging.h>