tests/storage/stream_flash: add nrf52840dk/nrf52840 to platform_allow

If nrf52840dk/nrf52840 is an integration platform, it should also be an
allowed platform, otherwise the test run breaks down.

Signed-off-by: Ilya Tagunov <[email protected]>

Author: tagunil

tests/subsys/storage/stream/stream_flash/testcase.yaml

@@ -7,6 +7,8 @@ common:
 tests:
   storage.stream_flash:
     tags: stream_flash
+    platform_allow:
+      - nrf52840dk/nrf52840
     integration_platforms:
       - nrf52840dk/nrf52840
   storage.stream_flash.simulator.no_explicit_erase: