Add Moodle 3.9.0 upgrade line to all the upgrade.php scripts

1) Check that all the " Command(s) to detect ..." in the description of the issue work as expected (no occurrences normally, some cases or exceptions allowed in some of them...) 2) Check all upgrade scripts have the 3.9.0 comment before the return with: find . -ipath '*/db/upgrade.php' | xargs grep -B4 'return true;' Random exceptions: Some upgrade scripts could be missing the comments before the return. Surely it's because some new steps already have been introduced after release. Verify the comments are present in the correct place (before those new steps). 3) This should return nothing too or the same exceptions as in step 2: for u in `find . -name upgrade.php | grep 'db/upgrade'`; do grep -B4 'return true;' "$u" | grep "Automatically generated" > /dev/null; if [ $? -ne 0 ]; then echo "$u"; fi ; done 4) Verify that the differences between the stable branch and master continue being 100% the same after the patch than before it (aka. the patch is 100% the same for both branches). 5) rock on.