ci: add ubsan suppression for simplicity sha256.c

ubsan detects when a left shift would overflow an integer type. This is
not UB (it would be if you tried to shift more than the type's width in
one shot) but "may be unintentional" and is therefore detected.

Add a whitelist to the giant list of whitelists.

Author: apoelstra

test/sanitizer_suppressions/ubsan

@@ -79,3 +79,4 @@ implicit-integer-sign-change:blech32.cpp
 implicit-integer-sign-change:primitives/block.h
 implicit-integer-sign-change:primitives/confidential.cpp
 implicit-integer-sign-change:primitives/confidential.h
+shift-base:simplicity/sha256.c