gcov CI broken

[bigerl]

see workflow run: https://github.com/rdf4cpp/rdf4cpp/actions/runs/8136991654/job/22234386121?pr=247

The log mentions a related issue in gcov and suggests a workaround:

(WARNING) Exception during parsing:
NegativeHits: Got negative hit value in gcov line 'branch 1 taken -1 (fallthrough)' caused by a bug in gcov tool, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68080. Use option --gcov-ignore-parse-errors with a value of negative_hits.warn, or negative_hits.warn_once_per_file.
(WARNING) Exception during parsing:
NegativeHits: Got negative hit value in gcov line 'branch 1 taken -1' caused by a bug in gcov tool, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68080. Use option --gcov-ignore-parse-errors with a value of negative_hits.warn, or negative_hits.warn_once_per_file.