gh-102856: Allow comments inside multi-line f-string expresions

Author: cmaureir

Parser/tokenizer.c

@@ -1795,8 +1795,12 @@ tok_get_normal_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct t
 
         // We don't allow # inside a one-line f-string expr,
         // but we do in multi-line f-string expr
-        if (INSIDE_FSTRING(tok) && (tok->lineno == 1)) {
-            return MAKE_TOKEN(syntaxerror(tok, "f-string expression part cannot include '#'"));
+        if (INSIDE_FSTRING(tok) && (current_tok->f_string_quote_size == 1)) {
+            while (c != '\n') {
+                c = tok_nextc(tok);
+                if (c == '}')
+                    return MAKE_TOKEN(syntaxerror(tok, "single line f-string expression part cannot include '#'"));
+            }
         }
 
         const char *prefix, *p, *type_start;