selftests: hid: fix vmtests.sh not running make headers

According to commit 01d6c48a82 ("Documentation: kselftest:
"make headers" is a prerequisite"), running the kselftests requires
to run "make headers" first.

Do that in "vmtest.sh" as well to fix the HID CI.

Link: https://lore.kernel.org/r/20230709-fix-selftests-v1-1-57d0878114cc@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

tools/testing/selftests/hid/vmtest.sh

@@ -79,6 +79,7 @@ recompile_kernel()
 	cd "${kernel_checkout}"
 
 	${make_command} olddefconfig
+	${make_command} headers
 	${make_command}
 }