Merge pull request #16238 from keszybz/set-handling-more

Fix handling of cases where a duplicate item is added to a set and related cleanups

diff --cc src/core/dbus-execute.c
Simple merge

diff --cc src/core/load-fragment.c
Simple merge

diff --cc src/core/manager.c
Simple merge

diff --cc src/journal/journalctl.c
Simple merge

diff --cc src/network/networkd-link.c
Simple merge

diff --cc src/resolve/resolved-dns-query.c
Simple merge

diff --cc src/resolve/resolved-dns-scope.c
Simple merge

diff --cc src/shared/userdb.c
Simple merge

diff --cc src/tmpfiles/tmpfiles.c
Simple merge