docs: remove double quote for env_filter directive comment

[leavesster]

Motivation

The docs about env_filter about target[span{field=value}]=level Directives has some type error.

the [script{source=\"stdout\"]=trace won't match the log below:

2025-01-14T08:54:02.550867Z  INFO script{source="stdout"}: trac: output to stdout: 131

but [script{source=stdout]=trace will match.

It seems the double quote will be part of the field's value.

Solution

just remove double quote and \