Fix line number in error message

Author: mdboom

Lib/test/test_source_encoding.py

@@ -252,7 +252,7 @@ def check(content):
             # not via a signal.
             self.assertGreaterEqual(rc, 1)
             self.assertIn(b"Non-UTF-8 code starting with", stderr)
-            self.assertIn(b"on line 5", stderr)
+            self.assertIn(b"on line 4", stderr)
 
         # continuation bytes in a sequence of 2, 3, or 4 bytes
         continuation_bytes = [bytes([x]) for x in range(0x80, 0xC0)]

Parser/tokenizer.c

@@ -564,7 +564,7 @@ ensure_utf8(char *line, struct tok_state *tok)
                      "in file %U on line %i, "
                      "but no encoding declared; "
                      "see https://peps.python.org/pep-0263/ for details",
-                     badchar, tok->filename, tok->lineno + 1);
+                     badchar, tok->filename, tok->lineno);
         return 0;
     }
     return 1;