Field names cannot begin with the $ character

### Expected Behavior

Ask to rename the variable

### Actual Behavior

through exception and can't import

### Reproduction Steps

_No response_

### Is there an existing issue for this?

- [x] I have searched the [issue tracker](https://www.github.com/Kong/insomnia/issues) for this problem.

### Which sync method do you use?

- [ ] Git sync.
- [ ] Insomnia Cloud sync.
- [x] Local only

### Additional Information

_No response_

### Insomnia Version

11.3.0

### What operating system are you using?

Windows

### Operating System Version

windows 11

### Installation method

download from website

### Last Known Working Insomnia version

_No response_

Reproduce the import failure on Windows 11 with Insomnia 11.3.0 using a field name that begins with `$`, then inspect the resulting exception and import path. The issue is done when the importer asks to rename the variable and the import can complete successfully.

Written by the indexing model from the issue text.