gcovr: Fix config file

gcovr 7.0 fixed a config file parsing bug [0].
Valid options are 'all', 'negative_hits.warn',
'negative_hits.warn_once_per_file'.

[0] https://github.com/gcovr/gcovr/pull/816

gcovr.cfg

 exclude = .*/tests/.*
 exclude = .*/tools/.*
 exclude = .*/include/common/dump.h
-gcov-ignore-parse-errors = yes
+gcov-ignore-parse-errors = negative_hits.warn