6.3 release preparation

[johanib]

In order to prepare for the 6.3 release, perform some checks:

• Check if all changes from the latest 6.2 tag are also in main.
• Double check that 6.3 contains the switch from 'teams' to 'invite'.
• Make a 6.3.x version, without -beta in the name
• Apply the needed security patches to the main branch.

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There are no changes in the 6.2.8 tag which are missing in main.

main...6.2.8

This comparison is somewhat confusing, as it seems code is missing from main. But on inspection, these changes are already applied on main, but with different commit hashes.