Fix `fastcov` invocation when zeroing counters

The selected `gcov` binary was not used which could lead to errors

CMakeLists.txt

@@ -371,7 +371,7 @@ if("${CMAKE_BUILD_TYPE}" STREQUAL "Coverage")
       ALL # in coverage mode we do coverage!
 
       # zero all counters
-      COMMAND ${FASTCOV} -q -z
+      COMMAND ${FASTCOV} -q -z --gcov "${GCOV_BIN}"
 
       # Run tests
       COMMAND ${CMAKE_CTEST_COMMAND}