MAINTAINERS: Add ubsan.h to the UBSAN section

The "ubsan.h" file was missed in the creation of the UBSAN section. Add
it.

Link: https://lore.kernel.org/r/20240424162722.work.576-kees@kernel.org
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: kees

MAINTAINERS

@@ -22651,6 +22651,7 @@ F:	include/linux/ubsan.h
 F:	lib/Kconfig.ubsan
 F:	lib/test_ubsan.c
 F:	lib/ubsan.c
+F:	lib/ubsan.h
 F:	scripts/Makefile.ubsan
 K:	\bARCH_HAS_UBSAN\b