Fix upgrade path for timescaledb extension

[maurerle]

Description

Before, the docs described to upgrade timescaledb extensions to a version, which would be incompatible with the mentioned PG13 version

Links

The description on the docs on this page:
https://docs.timescale.com/self-hosted/latest/upgrades/upgrade-pg/#upgrade-your-postgresql-instance
Did not match the information of the table..?

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[billy-the-fish]

Nice spot @maurerle, thank you.