chore: mark optional_bignum as supported

Makefile

@@ -25,7 +25,7 @@ TEST_OBJECTS := $(patsubst %.cxx, .build/%.o, $(TEST_SOURCES))
 TEST_BINARIES := .build/bin/selfvalidate
 
 EXCLUDED_TESTS := format* content ecmascript_regex \
-		  bignum float_overflow zeroTerminatedFloats
+		  float_overflow zeroTerminatedFloats
 EXCLUDED_TESTS := $(shell printf ":*optional_%s" $(EXCLUDED_TESTS) | cut -c2-)
 
 all: run-test