test/datareposinK: timing error in test case

test/datareposinK: timing error in test case

Occasionally, in github-action CI, datareposink.writeFlexibleTensors_n
fails due to synchronization errors:

```
[ RUN      ] datareposink.writeFlexibleTensors_n
../tests/nnstreamer_datarepo/unittest_datareposink.cc:570: Failure
Expected: (file_info) != (nullptr), actual: NULL vs (nullptr)
[  FAILED  ] datareposink.writeFlexibleTensors_n (173 ms)
```

It happens when the pipeline is set NULL before the file 'flexible.data'
is writtn within the pipeline.
Allow some time (0.1s) before setting it NULL.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>