sandbox: enable CONFIG_EFI_CAPSULE_AUTHENTICATE

Without CONFIG_EFI_CAPSULE_AUTHENTICATE=y the following tests are skipped:

* test/py/tests/test_efi_capsule/test_capsule_firmware_signed_fit.py
* test/py/tests/test_efi_capsule/test_capsule_firmware_signed_raw.py

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index e9fcc5b..8c2bcea 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -226,6 +226,7 @@
 CONFIG_EFI_RUNTIME_UPDATE_CAPSULE=y
 CONFIG_EFI_CAPSULE_ON_DISK=y
 CONFIG_EFI_CAPSULE_FIRMWARE_FIT=y
+CONFIG_EFI_CAPSULE_AUTHENTICATE=y
 CONFIG_UNIT_TEST=y
 CONFIG_UT_TIME=y
 CONFIG_UT_DM=y