support/testing/tests/boot/test_grub.py: use glibc toolchain

Since the recent bump of Bootlin toolchains in
947dbc92a20c5acea7882166cae7893e6ea661e1 ("toolchain/toolchain-external/toolchain-external-bootlin:
update to Bootlin toolchains 2025.08-1"), our grub2 tests are failing
as the new uClibc toolchains based on gcc 14.x have an issue building
grub.

Until this issue gets fixed at the uClibc level and since anyway glibc
is now the default in Buildroot, let's switch to using glibc
toolchains.

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/10972858692
  https://gitlab.com/buildroot.org/buildroot/-/jobs/10972858686
  https://gitlab.com/buildroot.org/buildroot/-/jobs/10972858680

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

support/testing/tests/boot/test_grub.py

@@ -8,7 +8,7 @@ class TestGrubi386BIOS(infra.basetest.BRTest):
         """
         BR2_x86_core2=y
         BR2_TOOLCHAIN_EXTERNAL=y
-        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_CORE2_UCLIBC_STABLE=y
+        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_CORE2_GLIBC_STABLE=y
         BR2_ROOTFS_POST_BUILD_SCRIPT="board/pc/post-build.sh {}"
         BR2_ROOTFS_POST_IMAGE_SCRIPT="support/scripts/genimage.sh"
         BR2_ROOTFS_POST_SCRIPT_ARGS="-c board/pc/genimage-bios.cfg"
@@ -37,7 +37,7 @@ class TestGrubi386EFI(infra.basetest.BRTest):
         """
         BR2_x86_core2=y
         BR2_TOOLCHAIN_EXTERNAL=y
-        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_CORE2_UCLIBC_STABLE=y
+        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_CORE2_GLIBC_STABLE=y
         BR2_ROOTFS_POST_BUILD_SCRIPT="board/pc/post-build.sh {}"
         BR2_ROOTFS_POST_IMAGE_SCRIPT="board/pc/post-image-efi.sh"
         BR2_LINUX_KERNEL=y
@@ -88,7 +88,7 @@ class TestGrubX8664EFI(infra.basetest.BRTest):
         BR2_x86_64=y
         BR2_x86_corei7=y
         BR2_TOOLCHAIN_EXTERNAL=y
-        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_64_UCLIBC_STABLE=y
+        BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_X86_64_GLIBC_STABLE=y
         BR2_ROOTFS_POST_BUILD_SCRIPT="board/pc/post-build.sh {}"
         BR2_ROOTFS_POST_IMAGE_SCRIPT="board/pc/post-image-efi.sh"
         BR2_LINUX_KERNEL=y