tests: kernel: gen_isr_table: exclude nrf9280pdk/nrf9280/cpuppr

First, SoC is not supported, but when I tried to add it, build results
in RAM overflow of ~10K. Excluding the platform for now, so CI is happy.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

tests/kernel/gen_isr_table/testcase.yaml

@@ -72,6 +72,7 @@ tests:
     platform_exclude:
       - m2gl025_miv
       - adp_xc7k/ae350
+      - nrf9280pdk/nrf9280/cpuppr
     filter: CONFIG_RISCV_PRIVILEGED
     extra_configs:
       - CONFIG_GEN_IRQ_VECTOR_TABLE=y