sdbusplus: include headers in SDK

Change-Id: Iad5fa91a6aa47b4ef0ea96ef86c6b299f74be814
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend b/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
index 2bbb39a..b21e2d0 100644
--- a/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
+++ b/common/recipes-core/packagegroups/packagegroup-core-standalone-sdk-target.bbappend
@@ -1 +1 @@
-RRECOMMENDS_${PN}_append = " gtest"
+RRECOMMENDS_${PN}_append = " gtest sdbusplus"