qemu: bump default testing version

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

src/tests/qemu/Makefile

diff --git a/src/tests/qemu/Makefile b/src/tests/qemu/Makefile
index 036f331..4efecd3 100644
--- a/src/tests/qemu/Makefile
+++ b/src/tests/qemu/Makefile
@@ -15,7 +15,7 @@
 ARCH := $(firstword $(subst -, ,$(CBUILD)))
 
 # Set these from the environment to override
-KERNEL_VERSION ?= 5.5.14
+KERNEL_VERSION ?= 5.4.77
 KERNEL_VERSION := $(KERNEL_VERSION)$(if $(DEBUG_KERNEL),$(if $(findstring -debug,$(KERNEL_VERSION)),,-debug),)
 BUILD_PATH ?= $(PWD)/../../../qemu-build/$(ARCH)
 DISTFILES_PATH ?= $(PWD)/distfiles