build-unit-test-docker: Add function2 to stdplus

Header only upgrade for uses of std::function that can be converted.

Change-Id: I5f43a461c0446258c5456055569a6ed8c3c4d229
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 389cb3c..153dd80 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -254,7 +254,7 @@
         ],
     ),
     "openbmc/stdplus": PackageDef(
-        depends=["fmtlib/fmt", "google/googletest"],
+        depends=["fmtlib/fmt", "Naios/function2", "google/googletest"],
         build_type="meson",
         config_flags=[
             "-Dexamples=false",