Backport: release only works if added to the end of an MR description

The documentation in ReleaseHotFix.md states:

You can bring this commit to release by adding to any empty line of the MR description box the following directive.

Backport: release

This is not true. You have to put the Backport: release on the last line of the MR description.

More precisely, all commands need to be the last text of the description. This is from @ben.boeckel in a discussion on !2779 (merged):

The Backport: (and any command really) are searched for from the end of the content. Ignoring empty lines and after stripping trailing space, if the line does not match <key>: <value>, it determines "I've hit the arbitrary content part" and ignores all previous lines.