On glossary update: do not reject a proposal for an explanation update if the glossary term translation does not change

### Describe the issue

[written in I-form for legibility]

I tried to add an additional explanation to a glossary for a given translation project. This specific glossary entry had a "correct" translation.

As a flyby-contributer, I tried to add an additional explanation to a given glossary entry. However when I tried to do so, I was presented with a red box with the message `Your suggestion is similar to the current translation!`

This is very unhelpful. The explanation is additional information that is necessary for a translator to understand if the glossary entry's suggested translation is applicable.

Upon reading the docs some more, I was surprised to see a `variant` option, which sounds like it it intended for listing multiple possible translations for a given string. Sounds like this should be more visible for flyby contributors to propose to a project.

### I already tried

- [x] I've read and searched [the documentation](https://docs.weblate.org/).
- [x] I've searched for similar filed issues in this repository.

### Steps to reproduce the behavior

Submit a glossary term update as a suggestion, by changing the contents of "Translation explanation", but do not change the target translation.

### Expected behavior

I can propose an update on the translation explanation.

### Screenshots

_No response_

### Exception traceback

```pytb

```

### How do you run Weblate?

Other

### Weblate version

2026.8.1 (codeberg instance)

### Weblate deploy checks

```shell
n.v.t.
```

### Additional context

_No response_

Start by reproducing the glossary suggestion flow described in the issue: change only "Translation explanation" while leaving the target translation unchanged, and inspect the validation that reports "Your suggestion is similar to the current translation!". Check the documented `variant` option for related behavior. Done means an explanation-only glossary update can be proposed without changing the term translation.

Written by the indexing model from the issue text.