Avoid consuming newline for unterminated string (#12067)

## Summary

This PR fixes the lexer logic to **not** consume the newline character
for an unterminated string literal.

Currently, the lexer would consume it to be part of the string itself
but that would be bad for recovery because then the lexer wouldn't emit
the newline token ever. This PR fixes that to avoid consuming the
newline character in that case.

This was discovered during https://github.com/astral-sh/ruff/pull/12060.

## Test Plan

Update the snapshots and validate them.

crates/ruff_python_parser/tests/snapshots/invalid_syntax@implicitly_concatenated_unterminated_string.py.snap

@@ -160,6 +160,15 @@ Module(
   |
 
 
+  |
+1 | 'hello' 'world
+  |               ^ Syntax Error: Expected a statement
+2 | 1 + 1
+3 | 'hello' f'world {x}
+4 | 2 + 2
+  |
+
+
   |
 1 | 'hello' 'world
 2 | 1 + 1

crates/ruff_python_parser/tests/snapshots/invalid_syntax@re_lexing__fstring_format_spec_1.py.snap

@@ -335,8 +335,8 @@ Module(
   |
 5 | f'middle {'string':\
 6 |         'format spec'}
+  |                       ^ Syntax Error: Expected a statement
 7 | 
-  | ^ Syntax Error: Expected a statement
 8 | f'middle {'string':\\
 9 |         'format spec'}
   |