all: Use stdplus::print over std::fprintf

Replacing `std::fprintf` with `stdplus::print`.
No logical change.

Tested: Buildable.
Signed-off-by: Michael Shen <gpgpgp@google.com>
Change-Id: I7050885c13e33244a4128aa519d163fd5b725098
diff --git a/test/handler_unittest.cpp b/test/handler_unittest.cpp
index b385321..549f1d0 100644
--- a/test/handler_unittest.cpp
+++ b/test/handler_unittest.cpp
@@ -21,6 +21,7 @@
 #include <nlohmann/json.hpp>
 #include <sdbusplus/message.hpp>
 #include <sdbusplus/test/sdbus_mock.hpp>
+#include <stdplus/print.hpp>
 
 #include <charconv>
 #include <filesystem>
@@ -164,12 +165,13 @@
 
 ACTION_P(TraceDbus, msg)
 {
-    std::fprintf(stderr, "%s\n", msg);
+    stdplus::print(stderr, "{}\n", msg);
 }
 
 ACTION_P(TraceDbus2, msg)
 {
-    std::fprintf(stderr, "%s(%02x)\n", msg, *static_cast<const uint8_t*>(arg2));
+    stdplus::print(stderr, "{}({:02x})\n", msg,
+                   *static_cast<const uint8_t*>(arg2));
 }
 
 constexpr char object_path[] = "/com/google/customAccel/test/path";