system() does not return boolean when Dir.pwd is uri:classloader 

### Environment

tested a few 9.x.x.x versions which all behave the same on MacOS

### Expected Behavior

```
$ bin/jruby -C uri:classloader:/ -e 'puts Dir.pwd; puts system("echo asd").class'
uri:classloader:/
asd
TrueClass
```

### Actual Behavior

```
$ bin/jruby -C uri:classloader:/ -e 'puts Dir.pwd; puts system("echo asd").class'
uri:classloader:/
NilClass
```
