Yes, mixing and matching vaccines has been fairly common at German vaccination centers. Last week, even the Chancellor Angela Merkel has also got Moderna as a second vaccine jab where as she received AstraZeneca shots earlier this year. This news is already in press.
For info: https://www.thelocal.de/20210625/covid-vaccine-mix-and-match-why-is-it-so-common-in-germany-and-is-it-safe/