doc: add app test package deps to readme

Author: johnny9

README.md

@@ -70,6 +70,8 @@ In addition the following dependencies are required for the GUI and tests:
 
 ```
 sudo apt install \
+  libgmock-dev \
+  libgtest-dev \
   qt6-base-dev \
   qt6-base-dev-tools \
   qt6-tools-dev \