test: correct architecture in EFI FIT test

On arm64 the its we use to generate the test FIT image has

	arch = "arm";

We should use "arm64" here which is mapped to IH_ARCH_ARM64 via
uimage_arch[].

Fixes: 8391f955494e ("test/py: Create a test for launching UEFI binaries from FIT images")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/test/py/tests/test_efi_fit.py b/test/py/tests/test_efi_fit.py
index 7b7c98f..0ad4835 100644
--- a/test/py/tests/test_efi_fit.py
+++ b/test/py/tests/test_efi_fit.py
@@ -431,6 +431,11 @@
     cons = u_boot_console
     # Array slice removes leading/trailing quotes.
     sys_arch = cons.config.buildconfig.get('config_sys_arch', '"sandbox"')[1:-1]
+    if sys_arch == 'arm':
+        arm64 = cons.config.buildconfig.get('config_arm64')
+        if arm64:
+            sys_arch = 'arm64'
+
     is_sandbox = sys_arch == 'sandbox'
 
     if is_sandbox: