selftests/bpf: Fixes for test_maps test

BPF CI has failed 3 times in the last 24 hours. Add retry for ENOMEM.
It's similar to the optimization plan:
commit 2f553b03 ("selftsets/bpf: Retry map update for non-preallocated per-cpu map")

Failed CI:
https://github.com/kernel-patches/bpf/actions/runs/13549227497/job/37868926343
https://github.com/kernel-patches/bpf/actions/runs/13548089029/job/37865812030
https://github.com/kernel-patches/bpf/actions/runs/13553536268/job/37883329296



selftests/bpf: Fixes for test_maps test
Fork 100 tasks to 'test_update_delete'
Fork 100 tasks to 'test_update_delete'
Fork 100 tasks to 'test_update_delete'
Fork 100 tasks to 'test_update_delete'
......
test_task_storage_map_stress_lookup:PASS
test_maps: OK, 0 SKIPPED

Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Link: https://lore.kernel.org/r/20250227142646.59711-4-jiayuan.chen@linux.dev


Signed-off-by: Alexei Starovoitov <ast@kernel.org>