support/testing: TestATFAllwinner needs python3 for u-boot

New U-Boot version needs Python 3.x for pylibfdt.

Fixes:
- https://gitlab.com/buildroot.org/buildroot/-/jobs/1019385909

Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

support/testing/tests/boot/test_atf.py

@@ -44,6 +44,7 @@ class TestATFAllwinner(infra.basetest.BRTest):
         BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2020.10"
         BR2_TARGET_UBOOT_BOARD_DEFCONFIG="bananapi_m64"
         BR2_TARGET_UBOOT_NEEDS_DTC=y
+        BR2_TARGET_UBOOT_NEEDS_PYTHON3=y
         BR2_TARGET_UBOOT_NEEDS_PYLIBFDT=y
         BR2_TARGET_UBOOT_NEEDS_ATF_BL31=y
         BR2_TARGET_UBOOT_FORMAT_CUSTOM=y