I just noticed a subtle discrepancy between the old parser and the PEG parser.

Consider this syntax error:
```
if x {a}: pass
```
The old parser places the caret at the '{':
```
$ python3.8 -c 'if x { a } : pass'
  File "<string>", line 1
    if x { a } : pass
         ^
SyntaxError: invalid syntax
```
The PEG parser puts it at 'a':
```
$ python3.10 -c 'if x { a } : pass'
  File "<string>", line 1
    if x { a } : pass
           ^
SyntaxError: invalid syntax
```

I don't think we should put much effort into fixing it -- it's just a curiosity. I suspect it's got to do with some lookahead.