testsuite: coverage: Correct value of GCOV_COUNTERS for gcc 14

number of counters have changed in gcc 14 by commit
https://github.com/gcc-mirror/gcc/commit/08a52331803



Specifically, a new counter was added in gcc/gcov-counter.def:
```
/* Conditions.  The counter is interpreted as a bit-set.  */
DEF_GCOV_COUNTER(GCOV_COUNTER_CONDS, "conditions", _ior)
```

which in turn updates the value of GCOV_COUNTERS that is defined in
gcov-io.h like this:
```
enum {
GCOV_COUNTERS
};
```

Signed-off-by: Roman Studenikin <srv@meta.com>