Add 500 branch to fork update script

This change is already in the 5.0 dev docs.

Author: leonstr

docs/guides/git/index.md

@@ -126,7 +126,7 @@ The following commands can be used to keep the your forked Moodle branches at yo
 ```
 #!/bin/bash
 git fetch upstream
-for BRANCH in MOODLE_{19..39}_STABLE MOODLE_{310..311}_STABLE MOODLE_{400..405}_STABLE main; do
+for BRANCH in MOODLE_{19..39}_STABLE MOODLE_{310..311}_STABLE MOODLE_{400..405}_STABLE MOODLE_500_STABLE main; do
     git push origin refs/remotes/upstream/$BRANCH:refs/heads/$BRANCH
 done
 ```