Upgrades JUnit to version 5.11.x (#3069)

Due to a minor bug in JUnit 5.11.x (junit-team/junit5#4054), fields meta-annotated with multiple `@ExtendWith` annotations are no longer recognized.
We combine those annotations into single `@ExtendWith` annotations, which also looks better.

Closes #2843.

Note: the bug is already fixed and the fix will appear in version `5.11.3`.
8 files changed