Fix: do not consume quote look-ahead in f-string.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/literal/FormatStringLiteralNode.java

@@ -348,11 +348,12 @@ protected static int[][] createTokens(FormatStringLiteralNode node, StringPart[]
                                     boolean triple = false;
                                     boolean inString = true;
                                     index++;
-                                    if (index < len && startq == text.charAt(index)) {
-                                        index++;
-                                        if (index < len && startq == text.charAt(index)) {
+                                    if (index  < len && startq == text.charAt(index )) {
+                                        if (index + 1 < len && startq == text.charAt(index + 1)) {
                                             // we are in ''' or """ string
                                             triple = true;
+
+                                            // fully consume the quotes
                                             index++;
                                         } else {
                                             // we are in empty string "" or ''