fix(core): output/iframe made to the w3c standard

Not all browsers support the self closing iframe tag, according to the
w3c standard it's not self closing.
Merge pull request #7040 from jeabakker/iframe-w3c-standard

fix(core): output/iframe made to the w3c standard
fix(upgrade): use correct table prefixes on river upgrade script

Fixes #7033
Merge pull request #7053 from beck24/7033-dbprefix

fix(upgrade): use correct table prefixes on river upgrade script
chore(i18n): update translations
chore(release): v1.9.0-rc.5
Merge pull request #7057 from beck24/release-1.9.0-rc.5

Release 1.9.0 rc.5