tests/net/lib/http_server/hpack: Exclude native_posix

This test explicity enables the POSIX_API which is
not compatible with native_posix.
Let's exclude this target.

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

tests/net/lib/http_server/hpack/testcase.yaml

@@ -9,5 +9,8 @@ common:
   integration_platforms:
     - native_sim
     - qemu_x86
+  platform_exclude:
+    - native_posix
+    - native_posix/native/64
 tests:
   net.http.server.http2_hpack: {}