Allow multiple indented blocks in REPL (#6097)

There aren't any tests but being able to do nested for loops seems like
a pretty big win to me so I'm going to put up for review.

The original returned boolean clearly had **false positives** for
detecting bad errors for things like nested `if` and `for` statements.
What is less clear is if there are any **true positives** which I am no
longer catching with the updated return value.

Co-authored-by: Jack O'Connor <jack@jackoconnor.dev>

src/shell.rs

@@ -86,11 +86,7 @@ fn shell_exec(
                             continuing_block
                         } // && p.location.is_some()
                         ParseErrorType::OtherError(msg) => {
-                            if msg.starts_with("Expected an indented block") {
-                                continuing_block
-                            } else {
-                                true
-                            }
+                            !msg.starts_with("Expected an indented block")
                         }
                         _ => true, // !matches!(p, ParseErrorType::UnrecognizedToken(Tok::Dedent, _))
                     }