Lexer syntax errors point to the wrong span

[mitsuhiko]

Description

When working on #443 I noticed that syntax errors in the lexer point to wrong span

Reproduction steps

Try to parse the following template:

{{ 10_ }}

Additional helpful information:

• Version of minijinja: 1.0.15

What did you expect

syntax error: '_' may not occur at end of number (in err_bad_trailing_underscore.txt:1)
----------------------- err_bad_trailing_underscore.txt -----------------------
   1 > {{ 10_ }}
     i      ^ syntax error

Instead I got

syntax error: '_' may not occur at end of number (in err_bad_trailing_underscore.txt:1)
----------------------- err_bad_trailing_underscore.txt -----------------------
   1 > {{ 10_ }}
     i ^^ syntax error