Fix multiline lexer bug

Co-authored-by: Hyeonji-Ryu <cjstk3940@naver.com>

Lib/test/test_grammar.py

@@ -257,8 +257,6 @@ the \'lazy\' dog.\n\
         self.assertTrue(x is Ellipsis)
         self.assertRaises(SyntaxError, eval, ".. .")
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailure
     def test_eof_error(self):
         samples = ("def foo(", "\ndef foo(", "def foo(\n")
         for s in samples:

parser/src/lexer.rs

@@ -568,7 +568,7 @@ where
                     } else {
                         if (c == '\n' && !triple_quoted) || (is_bytes && !c.is_ascii()) {
                             return Err(LexicalError {
-                                error: LexicalErrorType::StringError,
+                                error: LexicalErrorType::Eof,
                                 location: self.get_pos(),
                             });
                         }
@@ -784,7 +784,7 @@ where
             // First of all, we need all nestings to be finished.
             if self.nesting > 0 {
                 return Err(LexicalError {
-                    error: LexicalErrorType::NestingError,
+                    error: LexicalErrorType::Eof,
                     location: tok_pos,
                 });
             }