Update fsverity+odsign protos to protobuf3.

Test: manual atest
Bug: 286984317
Change-Id: I9bcc1ad858b9076c1a08e9df06e15a599c28f92c
diff --git a/fsverity/Android.bp b/fsverity/Android.bp
index ce3b499..93b4d93 100644
--- a/fsverity/Android.bp
+++ b/fsverity/Android.bp
@@ -44,6 +44,7 @@
     name: "libfsverity_digests_proto_rust",
     crate_name: "fsverity_digests_proto",
     source_stem: "fsverity_digests_proto",
+    use_protobuf3: true,
     protos: [
         "fsverity_digests.proto",
     ],
diff --git a/ondevice-signing/proto/Android.bp b/ondevice-signing/proto/Android.bp
index 356e661..6b1e35f 100644
--- a/ondevice-signing/proto/Android.bp
+++ b/ondevice-signing/proto/Android.bp
@@ -37,6 +37,7 @@
     crate_name: "odsign_proto",
     protos: ["odsign_info.proto"],
     source_stem: "odsign_proto",
+    use_protobuf3: true,
     host_supported: true,
     apex_available: [
         "com.android.compos",