CI: Valgrind: Improve the skipping of traced child processes

CI: Valgrind: Improve the skipping of traced child processes

Use --trace-children-skip instead of --trace-children-skip-by-arg
so that the skipping is only done based on the executable names.
(--trace-children-skip-by-arg can match other args than argv[0].)

Update the list of executables to skip to match what the scripts run.

Do not skip bash or sh. If Valgrind didn't trace the shell, then the
xz and xzdec programs run by the shell wouldn't be analyzed either.

Fixes: 7e99856f66c0 ("CI: Speed up Valgrind job by using --trace-children-skip-by-arg=...")