Broken per-arch backend limit

[praiskup]

The builds_max_workers_arch_per_owner=s390x=4 limit applies to all architectures:

[2025-01-06 11:00:34,128][ DEBUG][PID:646316][backend.build_dispatcher][worker_manager.py:run:466] Task '8474088-fedora-rawhide-i386' skipped, limit info: 'arch_s390x_owner', counter: x86_64_@rocm-packagers-sig=4, s390x_@fedora-llvm-team=4, aarch64_@fedora-llvm-team=1, x86_64_packit=4, x86_64_averbyts=1, x86_64_xxmitsu=4, x86_64_@theforeman=1, x86_64_jwakely=4, aarch64_jwakely=4, ppc64le_jwakely=4, s390x_jwakely=4, s390x_packit=1, ppc64le_packit=1, aarch64_packit=1, aarch64_solopasha=3, x86_64_solopasha=3, x86_64_maximizerr=1, x86_64_nucleo=1, x86_64_psimovec=2, aarch64_psimovec=2, x86_64_eclipseo=4, x86_64_lbalhar=4, x86_64_osloup=4, s390x_osloup=4, aarch64_osloup=2, ppc64le_osloup=4, x86_64_whitehara=4, ppc64le_whitehara=4, s390x_whitehara=4, aarch64_whitehara=4, s390x_@yggdrasil=1, x86_64_stsp=2