@storchaka, as far as I know and can see from the repo, our policy has long been to not backport general documentation changes to security-fix-only branches, certainly long before we migrated to git. See, for example, changes made to the 3.4 branch after it went to security-fix mode. While release managers make occasional exceptions, the rule is as stated in the devguide:
The only changes made to a security branch are those fixing issues exploitable by attackers such as crashes, privilege escalation and, optionally, other issues such as denial of service attacks. Any other changes are not considered a security risk and thus not backported to a security branch. You should also consider fixing hard-failing tests in open security branches since it is important to be able to run the tests successfully before releasing.