CI: coverage build target fails

[kgiusti]

make coverage
...
Combining tracefiles.
.. found 2 files to aggregate.
Merging dispatch-base.info..1 remaining
lcov: ERROR: trace file 'dispatch-base.info' is empty
	(use "lcov --ignore-errors empty ..." to bypass this error)
lcov: ERROR: no valid records found in tracefile dispatch-total-raw.info
	(use "lcov --ignore-errors empty ..." to bypass this error)
genhtml: ERROR: no valid records found in tracefile dispatch-total.info
	(use "genhtml --ignore-errors empty ..." to bypass this error)
make[3]: *** [CMakeFiles/coverage.dir/build.make:70: CMakeFiles/coverage] Error 1
make[2]: *** [CMakeFiles/Makefile2:1045: CMakeFiles/coverage.dir/all] Error 2
make[1]: *** [CMakeFiles/Makefile2:1052: CMakeFiles/coverage.dir/rule] Error 2
make: *** [Makefile:543: coverage] Error 2