Retain malloc-failure mode for coverage checks

tests/cbmc/proofs/Makefile.common

@@ -267,7 +267,7 @@ CBMCFLAGS += $(CBMC_FLAG_FLUSH)
 # CBMC 6.0.0 enables all standard checks by default, which can make coverage analysis
 # very slow. See https://github.com/diffblue/cbmc/issues/8389
 # For now, we disable these checks when generating coverage info.
-COVERFLAGS ?= --no-standard-checks
+COVERFLAGS ?= --no-standard-checks --malloc-may-fail --malloc-fail-null
 
 # CBMC flags used for property checking