fix valgrid supressions for string

tests/valgrind.suppressions

@@ -76,4 +76,13 @@
    fun:strlen
    fun:bson_strdup
    ...
-}
\ No newline at end of file
+}
+{
+   temp_ignore_screate
+   Memcheck:Leak
+   ...
+   fun:*_S_create*
+   ...
+   fun:*_M_mutate*
+   ...
+}