Merge branch 'babolivier/fix-context-filter' of github.com:matrix-org/synapse...

Merge branch 'babolivier/fix-context-filter' of github.com:matrix-org/synapse into babolivier/fix-context-filter

changelog.d/6553.bugfix

-Fix a bug causing responses to the `/context` client endpoint to not use the pruned version of the event the request is for.
+Fix a bug causing responses to the `/context` client endpoint to not use the pruned version of the event.