test(ci): the CI replay does not run Git Bash under x64 emulation on Windows arm64

Mechanism: Git for Windows on arm64 ships native git.exe but an x86-64 MSYS
usr/bin/bash.exe, which runs under the WoA x64 emulator. With the os-tests
lane's 16 parallel workers, a replayed step's bash dies before running a line
with 0xC000026F (STATUS_WX86_INTERNAL_ERROR) or 0xC0000005 and empty
stdout/stderr, so an unmodified baseline replay fails as a bare
AssertionError (jobs 112635777217 and 112764629268, two different nodeids).

Repro (throwaway workflows on the real runners, previous commit's diagnostics):
- windows-latest-32-arm-core, 16 copies of the file's replay tests at once,
  4 rounds: 21/64 copies red, every failure 0xC000026F.
- Same load, windows-latest-32-core (x64): 0/64.
- Passing SYSTEMROOT/WINDIR or the full Windows env to the step: 12/48 and
  17/48 vs 15/48 base, so the stripped env is not the cause.
- One process, 32 threads, 600 replays: 0 crashes; it takes concurrent
  processes, i.e. host-wide emulator load.

Seam: _NATIVE_WINDOWS_TOO keeps platforms("linux", "windows") and adds a
skipif for win32 + native_arch() == arm64. The x64 Windows row still runs the
replay on the Windows layout (python.exe-only venv, Git Bash), Linux arm64
keeps it (native bash), and the routing guard that pins the marker passes.

tests/ci/test_update_ci_routing.py

@@ -32,6 +32,7 @@ from typing import Any
 
 import pytest
 
+from hermes_platform.host.facts import native_arch
 from tests.ci import _gha_expr as gha
 from tests.ci import workflow_steps
 
@@ -49,7 +50,19 @@ _spec.loader.exec_module(cc)
 # bash is Git Bash: the replay, its dispatch chain and the ineffective-step controls carry this
 # marker so a green Windows job has run them on that layout (review F81-R). Not "any": macOS
 # bash 3.2 is not a host the replay has been run on.
-_NATIVE_WINDOWS_TOO = pytest.mark.platforms("linux", "windows")
+_NATIVE_WINDOWS_PLATFORMS = pytest.mark.platforms("linux", "windows")
+# Not Windows on arm64: Git for Windows ships an x86-64 MSYS bash.exe there, run under emulation,
+# and with the os-tests lane's 16 workers it dies with 0xC000026F (STATUS_WX86_INTERNAL_ERROR) or
+# 0xC0000005 before running a line, on replays of unchanged workflows: one copy of this file red
+# in ~3 when 16 run at once, against 0/64 on x64 Windows under the same load. The emulator's
+# crash is not the replay's to assert on; the x64 Windows row runs the same layout natively.
+_EMULATED_BASH = pytest.mark.skipif(
+    sys.platform == "win32" and native_arch() == "arm64",
+    reason="Git Bash is x86-64 under emulation on Windows arm64 and crashes under parallel load")
+
+
+def _NATIVE_WINDOWS_TOO(test):
+    return _NATIVE_WINDOWS_PLATFORMS(_EMULATED_BASH(test))
 _lister_spec = importlib.util.spec_from_file_location("list_os_marked", _REPO / "scripts/ci/list_os_marked_tests.py")
 assert _lister_spec is not None and _lister_spec.loader is not None
 lister = importlib.util.module_from_spec(_lister_spec)