minus-suffixed types for commands with ignored errors

[Arfrever]

systemd 240 has this new feature (added here by this pull request):

        * tmpfiles.d/ line types may now be suffixed with a '-' character, in
          which case the respective line failing is ignored.

In tmpfiles.d(5) man page it is described:

The type consists of a single letter and optionally an exclamation mark and/or minus sign.
...
If the minus sign is used, this line failing to run successfully during create (and only create) will not cause the execution of systemd-tmpfiles to return an error.

For example:

# Modify sysfs but don't fail if we are in a container with a read-only /proc
w- /proc/sys/vm/swappiness - - - - 10