[nrf fromlist] tests: drivers: timer: Enable test on nRF54L* cpuflpr

Enable nrf_grtc_timer test on:
- nrf54l09pdk/nrf54l09/cpuflpr and
- nrf54l20pdk/nrf54l20/cpuflpr.

Upstream PR #: 87124

Signed-off-by: Sebastian Głąb <sebastian.glab@nordicsemi.no>

Author: nordic-segl

tests/drivers/timer/nrf_grtc_timer/testcase.yaml

@@ -3,12 +3,14 @@ tests:
     tags: drivers
     platform_allow:
       - nrf54l09pdk/nrf54l09/cpuapp
+      - nrf54l09pdk/nrf54l09/cpuflpr
       - nrf54l15dk/nrf54l15/cpuapp
       - nrf54l15dk/nrf54l15/cpuflpr
       - nrf54l15bsim/nrf54l15/cpuapp
       - nrf54h20dk/nrf54h20/cpuapp
       - nrf54h20dk/nrf54h20/cpurad
       - nrf54h20dk/nrf54h20/cpuppr
       - nrf54l20pdk/nrf54l20/cpuapp
+      - nrf54l20pdk/nrf54l20/cpuflpr
     integration_platforms:
       - nrf54l20pdk/nrf54l20/cpuapp