processors.rename - weird behaviour in regards to "tags"-option

### Relevant telegraf.conf with `rename` processor

```toml
[[inputs.mock]] # this input is always the same

metric_name = "mock"
[[inputs.mock.constant]]
name = "constant"
value = 123

[[processors.rename]]
namepass = ["mock"]
tags = { "test" = "doesnt_work" } # <-------- doesn't work but no error
```

### Logs from Telegraf

```text
$ telegraf -config tags.conf -test -test-wait 5 -debug
...
> mock,host=myhost constant=123i 1755612972000000000
```

The `tags` option seems to exist, though, as I get an error if I try to use an option that doesn't exist:

```toml
[[inputs.mock]] # this input is always the same

metric_name = "mock"
[[inputs.mock.constant]]
name = "constant"
value = 123

[[processors.rename]]
namepass = ["mock"]
thisdoesntexist = { "test" = "doesnt_work" } # <------------ error!
```

output:
```
$ telegraf -config tags.conf -test -test-wait 5 -debug

2025-08-19T14:20:39Z I! Loading config: tags.conf
2025-08-19T14:20:39Z E! loading config file tags.conf failed: plugin processors.rename: line 8: configuration specified the fields ["thisdoesntexist"], but they were not used; this is either a typo or this config option does not exist in this version
````

The `override`-processor behaves as expected, though:

```toml
[[inputs.mock]] # this input is always the same

metric_name = "mock"
[[inputs.mock.constant]]
name = "constant"
value = 123

[[processors.override]]
namepass = ["mock"]
tags = { "test" = "works" }
```

output:
```
$ telegraf -config tags.conf -test -test-wait 5 -debug
...
> mock,host=myhost,test=works constant=123i 1755613379000000000
```

### System info

Telegraf 1.34.4 (git: HEAD@e7ce1e1e), RHEL 9

### Steps to reproduce

Use "tags" option with `rename`-processor.

### Expected behavior

Expect that the tags are added to the metric

### Actual behavior

Observe that the tags aren't added to the metric