sifiveu: enable 6.18 testing kernel

The sifiveu target now supports 6.18 kernel as testing.

Signed-off-by: Zoltan HERPAI <wigyori@uid0.hu>

Author: wigyori

target/linux/sifiveu/Makefile

@@ -12,6 +12,7 @@ KERNELNAME:=Image dtbs
 SUBTARGETS:=generic
 
 KERNEL_PATCHVER:=6.12
+KERNEL_TESTING_PATCHVER:=6.18
 
 include $(INCLUDE_DIR)/target.mk