Make cheribsd-mfs-root-kernel default ignore build-bench-kernels

This was triggering an assertion in the test case that I just added.

pycheribuild/projects/cross/cheribsd.py

@@ -1830,7 +1830,6 @@ def default_kernel_config(self, platform: "Optional[ConfigPlatform]" = None, **f
             platform = self.get_default_kernel_platform()
         kernel_abi = filter_kwargs.pop("kernel_abi", self.get_default_kernel_abi())
         filter_kwargs.setdefault("caprevoke", self.caprevoke_kernel)
-        filter_kwargs.setdefault("benchmark", self.build_bench_kernels)
         filter_kwargs["mfsroot"] = True
         config = CheriBSDConfigTable.get_default(self.crosscompile_target, platform, kernel_abi, **filter_kwargs)
         return config.kernconf

tests/test_argument_parsing.py

@@ -921,6 +921,14 @@ def test_kernel_configs(target, config_options: "list[str]", expected_kernels: "
             ],
             ["CHERI-QEMU-MFS-ROOT"],
         ),
+        pytest.param("cheribsd-mfs-root-kernel-aarch64", [], ["GENERIC-MFS-ROOT"]),
+        # regression test for assert len(configs) != 0, "No matching default kernel configuration", the
+        # build-bench-kernels flag should not affect the default kernel config selection just the additional ones.
+        pytest.param(
+            "cheribsd-mfs-root-kernel-aarch64",
+            ["--cheribsd/build-bench-kernels", "--cheribsd/default-kernel-abi=hybrid"],
+            ["GENERIC-MFS-ROOT"],
+        ),
     ],
 )
 def test_mfsroot_kernel_configs(target: str, config_options: "list[str]", expected_kernels: "list[str]"):