Migrate from /var/run/pesign to /run/pesign

[mika]

Forwarding this from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=964157:

Quoting from syslog:

| [...] systemd-tmpfiles[512]: [/usr/lib/tmpfiles.d/pesign.conf:1] Line references path below legacy directory /var/run/, updating /var/run/pesign → /run/pesign; please update the tmpfiles.d/ drop-in file accordingly.

AFAICT the /var/run/pesign should be replaced with /run/pesign.
FTR, it's not just present in /usr/lib/tmpfiles.d/pesign.conf but in several places of the source code, should maybe get adjusted to follow current best practices?