Upgrade vendor libraries

[lippserd]

I think that upgrading our vendor dependencies has often been forgotten and should definitely be included in our release workflow. Since some upgrades are available, I would include them in the next bugfix release:

Library	Current Version	Upstream Version
dompdf	1.2.1 (2022-03-24)	1.2.2 (2022-04-27) or 2.0.0 (2022-06-21)
HTMLPurifier	4.10.0 (2018-03-23)	4.14.0 (2021-12-25)
Parsedown	1.7.3 (2019-04-02)	1.7.4 (2019-12-30)