Add Sytest/Complement coverage to scheduled runs (#2962)

This adds Sytest and Complement coverage reporting to the nightly
scheduled CI runs.

Fixes a few API mode related issues as well, since we seemingly never
really ran them with Complement.

Also fixes a bug related to device list changes: When we pass in an
empty `newlyLeftRooms` slice, we got a list of all currently joined
rooms with the corresponding members. When we then got the
`newlyJoinedRooms`, we wouldn't update the `changed` slice, because we
already got the user from the `newlyLeftRooms` query. This is fixed by
simply ignoring empty `newlyLeftRooms`.

.github/workflows/dendrite.yml

@@ -460,7 +460,8 @@ jobs:
         name: Run Complement Tests
         env:
           COMPLEMENT_BASE_IMAGE: complement-dendrite:${{ matrix.postgres }}${{ matrix.api }}${{ matrix.cgo }}
-          API: ${{ matrix.api && 1 }}
+          COMPLEMENT_DENDRITE_API: ${{ matrix.api && 1 }}
+          COMPLEMENT_SHARE_ENV_PREFIX: COMPLEMENT_DENDRITE_
         working-directory: complement
 
   integration-tests-done: