samples/posix/env: Change integration platform

There is some instability problems with qemu_riscv32
#72858
which cause this sample test to fail in CI at random.
Let's change the integration platform to a reliable one,
so this test focuses on the sample and does not produce
false test failures due to the platform.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>

Author: aescolar

samples/posix/env/sample.yaml

@@ -7,7 +7,7 @@ common:
     - native_posix
     - native_posix/native/64
   integration_platforms:
-    - qemu_riscv32
+    - native_sim
   harness: console
   harness_config:
     type: multi_line