[appmgr] Temporarily disable UBSan for data_file_reader_writer

UBSan was reporting a misaligned member access. Disable UBSan for this
target for now, then we will come back to fix it once asan-ubsan is
migrated into CQ.

Bug: 44385
Change-Id: I9510f3481f932c65cacd6cc52e2efa88623060be
diff --git a/src/sys/appmgr/integration_tests/util/BUILD.gn b/src/sys/appmgr/integration_tests/util/BUILD.gn
index 2bc11fd..caf9f04 100644
--- a/src/sys/appmgr/integration_tests/util/BUILD.gn
+++ b/src/sys/appmgr/integration_tests/util/BUILD.gn
@@ -33,6 +33,10 @@
     "//sdk/lib/sys/cpp/testing:integration",
     "//src/lib/fxl",
   ]
+
+  # TODO(44385): UBSan has found an instance of undefined behavior in this target.
+  # Disable UBSan for this target temporarily until it is migrated into CI/CQ.
+  configs += [ "//build/config:temporarily_disable_ubsan_do_not_use" ]
 }
 
 executable("persistent_storage_test_util_bin") {