common: test: Add gmock dependency to generated targets

Fixes the following error when building with gmock supplied by
subproject:

```
FAILED: common/test/pldm_utils_test.p/pldm_utils_test.cpp.o
ccache c++ -Icommon/test/pldm_utils_test.p -I../subprojects/googletest/googletest/include -I../subprojects/googletest/googletest -Isubprojects/googletest/__CMake_build -I../subprojects/googletest/__CMake_build -Isubprojects/googletest -I../subprojects/googletest -Isubprojects/phosphor-dbus-interfaces/gen -I../subprojects/phosphor-dbus-interfaces/gen -I../subprojects/sdbusplus/include -Isubprojects/phosphor-logging/lib/include -I../subprojects/phosphor-logging/lib/include -I. -I.. -I/usr/include -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -Werror -std=c++23 -O2 -g -Wno-psabi -DLIBPLDMRESPONDER -DOEM_IBM -include /home/andrew/src/openbmc.org/openbmc/pldm/build/config.h -DBOOST_ASIO_DISABLE_THREADS -DBOOST_ALL_NO_LIB -DBOOST_SYSTEM_NO_DEPRECATED -DBOOST_ERROR_CODE_HEADER_ONLY -DBOOST_COROUTINES_NO_DEPRECATION_WARNING -pthread -isystem../subprojects/nlohmann_json/single_include -isystem../subprojects/libpldm/include -isystemsubprojects/libpldm/include -isystem../subprojects/googletest/googletest -isystem../subprojects/googletest/googletest/include -MD -MQ common/test/pldm_utils_test.p/pldm_utils_test.cpp.o -MF common/test/pldm_utils_test.p/pldm_utils_test.cpp.o.d -o common/test/pldm_utils_test.p/pldm_utils_test.cpp.o -c ../common/test/pldm_utils_test.cpp
In file included from ../common/test/pldm_utils_test.cpp:2:
../common/test/mocked_utils.hpp:3:10: fatal error: gmock/gmock.h: No such file or directory
    3 | #include <gmock/gmock.h>
      |          ^~~~~~~~~~~~~~~
compilation terminated.
```

Change-Id: I56cedd3df2d07f850fc0d13599ed52f99981e35b
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>