The permissions debian.supp differs depending on the umask of the build
environment:

https://tests.reproducible-builds.org/debian/rb-pkg/bookworm/amd64/diffoscope-results/valgrind.html

  -rw-r--r--···0·root·········(0)·root·········(0)·····1136·2022-08-28·10:40:16.000000·./usr/lib/valgrind/debian.supp
  vs.
  -rw-rw-r--···0·root·········(0)·root·········(0)·····1136·2022-08-28·10:40:16.000000·./usr/lib/valgrind/debian.supp


The attached patch to debian/rules explicitly sets the permissions on
debian.supp after dh_fixperms is run.

Another approach is to remove the exclusion on .supp files from the
dh_fixperms call, though presumeably this was added for a reason and
that might need to be fixed some other way.

According to my local tests, with this patch applied valgrind should
build reproducibly on tests.reproducible-builds.org!

Thanks for maintaining valgrind!

live well,
  vagrant