fix some more miri errors

probably relevant to mthom/scryer-prolog#2438

src/machine/copier.rs

@@ -398,7 +398,6 @@ mod tests {
     use crate::machine::mock_wam::*;
 
     #[test]
-    #[cfg_attr(miri, ignore = "blocked on atom_table.rs UB")]
     fn copier_tests() {
         let mut wam = MockWAM::new();
 

src/machine/lib_machine.rs

@@ -292,7 +292,7 @@ mod tests {
     }
 
     #[test]
-    #[cfg_attr(miri, ignore)]
+    #[cfg_attr(miri, ignore = "blocked on streams.rs UB")]
     fn complex_results() {
         let mut machine = Machine::new_lib();
         machine.load_module_string(