py/repl: Fix handling of unmatched brackets and unfinished quotes.

Before this patch:

    >>> print(')
    ... ')
    Traceback (most recent call last):
      File "<stdin>", line 1
    SyntaxError: invalid syntax

After this patch:

    >>> print(')
    Traceback (most recent call last):
      File "<stdin>", line 1
    SyntaxError: invalid syntax

This matches CPython and prevents getting stuck in REPL continuation when a
1-quote is unmatched.

py/repl.c

@@ -106,8 +106,13 @@ bool mp_repl_continue_with_input(const char *input) {
         }
     }
 
-    // continue if unmatched brackets or quotes
-    if (n_paren > 0 || n_brack > 0 || n_brace > 0 || in_quote == Q_3_SINGLE || in_quote == Q_3_DOUBLE) {
+    // continue if unmatched 3-quotes
+    if (in_quote == Q_3_SINGLE || in_quote == Q_3_DOUBLE) {
+        return true;
+    }
+
+    // continue if unmatched brackets, but only if not in a 1-quote
+    if ((n_paren > 0 || n_brack > 0 || n_brace > 0) && in_quote == Q_NONE) {
         return true;
     }