More warnings about missing shell_exec() since Matomo 4.4.0 #17838

reported in
https://forum.matomo.org/t/warning-shell-exec-has-been-disabled-for-security-reasons-matomo-4-4-0/42661 (two users)
and
https://forum.matomo.org/t/error-after-update-to-v4-4-0/42679

It seems like this is maybe caused by https://github.com/matomo-org/matomo/pull/17576

It be good to add a function_exists('shell_exec') before these calls 👍 and also make sure warnings are suppressed using <a class='mention' href='https://github.com/shell_exec'>@shell_exec</a> 👍