fix the type of sort

[capfredf]

No description provided.

[samth]

This looks right but the new test doesn't pass.

[jessealama]

I recently bumped into this false positive type checking (that is, type checking passed but it should have failed). If I make the change here to my local TR, I get the expected type check error.

[dannypsnl]

I think this one failed because it raises two errors

Type Checker: Polymorphic function `sort' could not be applied to arguments:
...
Type Checker: Polymorphic function with keywords sort7 could not be applied to arguments:
...

a simple fix is changing to(exn-pred "Type Checker: Summary: 2 errors encountered"), but I have no idea if need to reduce to only report one error.

[samth]

It would be great to fix this before the release -- @capfredf do you want me to do that?

[capfredf]

Ah, I totally forgot this pending pull request. I will be working on those failed tests later today.