tests/functional/test_tuxrun: Restrict to TCG

The tuxrun tests specify the cortex-a57 CPU; this doesn't work on a
KVM-only QEMU build, where the default accelerator is KVM but KVM
doesn't support that CPU type.  Restrict the test to TCG, to avoid
failures on KVM-only AArch64 builds:
        Output: qemu-system-aarch64: kvm_init_vcpu: kvm_arch_init_vcpu failed (0): Invalid argument

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20260507194728.2034696-7-peter.maydell@linaro.org

tests/functional/aarch64/test_tuxrun.py

@@ -25,6 +25,7 @@ class TuxRunAarch64Test(TuxRunBaselineTest):
 
     def test_arm64(self):
         self.set_machine('virt')
+        self.require_accelerator('tcg')
         self.cpu='cortex-a57'
         self.console='ttyAMA0'
         self.wait_for_shutdown=False
@@ -40,6 +41,7 @@ def test_arm64(self):
 
     def test_arm64be(self):
         self.set_machine('virt')
+        self.require_accelerator('tcg')
         self.cpu='cortex-a57'
         self.console='ttyAMA0'
         self.wait_for_shutdown=False