Tag with @ as the first character does not work properly in Flux queries

__Steps to reproduce:__
List the minimal actions needed to reproduce the behavior.

1. Insert the following into Influx `my_measurement,@pre_quality=ok field=5i`
2. Write a flux query to fetch the values
```
from(bucket: "b")
|> range(start: 0)
|> filter(fn: (r) => r["_measurement"] == "my_measurement")
|> filter(fn: (r) => r["_field"] == "field")
|> filter(fn: (r) => r["@pre_quality"] == "ok")
```

__Expected behavior:__
The inserted value is returned

__Actual behavior:__
Nothing is returned.

If `$` is used instead of `@` it does work as expected.

__Environment info:__

* System info: Ubuntu 20.04
* InfluxDB version: 2.6.1
* Other relevant environment details: Container runtime, disk info, etc

__Config:__
Copy any non-default config values here or attach the full config as a gist or file.

__Logs:__
Include snippet of errors in log.

__Performance:__
Generate profiles with the following commands for bugs related to performance, locking, out of memory (OOM), etc.

Start by reproducing the issue in InfluxDB 2.6.1 using the provided line protocol and Flux query, then compare the @ tag with the working $ variant. Done means the query returns the inserted value when the tag name begins with @.

Written by the indexing model from the issue text.